Related
I would like to be able to get the name of a variable as a string but I don't know if Python has that much introspection capabilities. Something like:
>>> print(my_var.__name__)
'my_var'
I want to do that because I have a bunch of variables I'd like to turn into a dictionary like :
bar = True
foo = False
>>> my_dict = dict(bar=bar, foo=foo)
>>> print my_dict
{'foo': False, 'bar': True}
But I'd like something more automatic than that.
Python have locals() and vars(), so I guess there is a way.
As unwind said, this isn't really something you do in Python - variables are actually name mappings to objects.
However, here's one way to try and do it:
>>> a = 1
>>> for k, v in list(locals().iteritems()):
if v is a:
a_as_str = k
>>> a_as_str
a
>>> type(a_as_str)
'str'
I've wanted to do this quite a lot. This hack is very similar to rlotun's suggestion, but it's a one-liner, which is important to me:
blah = 1
blah_name = [ k for k,v in locals().iteritems() if v is blah][0]
Python 3+
blah = 1
blah_name = [ k for k,v in locals().items() if v is blah][0]
Are you trying to do this?
dict( (name,eval(name)) for name in ['some','list','of','vars'] )
Example
>>> some= 1
>>> list= 2
>>> of= 3
>>> vars= 4
>>> dict( (name,eval(name)) for name in ['some','list','of','vars'] )
{'list': 2, 'some': 1, 'vars': 4, 'of': 3}
This is a hack. It will not work on all Python implementations distributions (in particular, those that do not have traceback.extract_stack.)
import traceback
def make_dict(*expr):
(filename,line_number,function_name,text)=traceback.extract_stack()[-2]
begin=text.find('make_dict(')+len('make_dict(')
end=text.find(')',begin)
text=[name.strip() for name in text[begin:end].split(',')]
return dict(zip(text,expr))
bar=True
foo=False
print(make_dict(bar,foo))
# {'foo': False, 'bar': True}
Note that this hack is fragile:
make_dict(bar,
foo)
(calling make_dict on 2 lines) will not work.
Instead of trying to generate the dict out of the values foo and bar,
it would be much more Pythonic to generate the dict out of the string variable names 'foo' and 'bar':
dict([(name,locals()[name]) for name in ('foo','bar')])
This is not possible in Python, which really doesn't have "variables". Python has names, and there can be more than one name for the same object.
I think my problem will help illustrate why this question is useful, and it may give a bit more insight into how to answer it. I wrote a small function to do a quick inline head check on various variables in my code. Basically, it lists the variable name, data type, size, and other attributes, so I can quickly catch any mistakes I've made. The code is simple:
def details(val):
vn = val.__name__ # If such a thing existed
vs = str(val)
print("The Value of "+ str(vn) + " is " + vs)
print("The data type of " + vn + " is " + str(type(val)))
So if you have some complicated dictionary / list / tuple situation, it would be quite helpful to have the interpreter return the variable name you assigned. For instance, here is a weird dictionary:
m = 'abracadabra'
mm=[]
for n in m:
mm.append(n)
mydic = {'first':(0,1,2,3,4,5,6),'second':mm,'third':np.arange(0.,10)}
details(mydic)
The Value of mydic is {'second': ['a', 'b', 'r', 'a', 'c', 'a', 'd', 'a', 'b', 'r', 'a'], 'third': array([ 0., 1., 2., 3., 4., 5., 6., 7., 8., 9.]), 'first': [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]}
The data type of mydic is <type 'dict'>
details(mydic['first'])
The Value of mydic['first'] is (0, 1, 2, 3, 4, 5, 6)]
The data type of mydic['first'] is <type 'list'>
details(mydic.keys())
The Value of mydic.keys() is ['second', 'third', 'first']
The data type of mydic.keys() is <type 'tuple'>
details(mydic['second'][0])
The Value of mydic['second'][0] is a
The data type of mydic['second'][0] is <type 'str'>
I'm not sure if I put this in the right place, but I thought it might help. I hope it does.
I wrote a neat little useful function based on the answer to this question. I'm putting it here in case it's useful.
def what(obj, callingLocals=locals()):
"""
quick function to print name of input and value.
If not for the default-Valued callingLocals, the function would always
get the name as "obj", which is not what I want.
"""
for k, v in list(callingLocals.items()):
if v is obj:
name = k
print(name, "=", obj)
usage:
>> a = 4
>> what(a)
a = 4
>>|
I find that if you already have a specific list of values, that the way described by #S. Lotts is the best; however, the way described below works well to get all variables and Classes added throughout the code WITHOUT the need to provide variable name though you can specify them if you want. Code can be extend to exclude Classes.
import types
import math # mainly showing that you could import what you will before d
# Everything after this counts
d = dict(globals())
def kv_test(k,v):
return (k not in d and
k not in ['d','args'] and
type(v) is not types.FunctionType)
def magic_print(*args):
if len(args) == 0:
return {k:v for k,v in globals().iteritems() if kv_test(k,v)}
else:
return {k:v for k,v in magic_print().iteritems() if k in args}
if __name__ == '__main__':
foo = 1
bar = 2
baz = 3
print magic_print()
print magic_print('foo')
print magic_print('foo','bar')
Output:
{'baz': 3, 'foo': 1, 'bar': 2}
{'foo': 1}
{'foo': 1, 'bar': 2}
In python 3 this is easy
myVariable = 5
for v in locals():
if id(v) == id("myVariable"):
print(v, locals()[v])
this will print:
myVariable 5
Python3. Use inspect to capture the calling local namespace then use ideas presented here. Can return more than one answer as has been pointed out.
def varname(var):
import inspect
frame = inspect.currentframe()
var_id = id(var)
for name in frame.f_back.f_locals.keys():
try:
if id(eval(name)) == var_id:
return(name)
except:
pass
Here's the function I created to read the variable names. It's more general and can be used in different applications:
def get_variable_name(*variable):
'''gets string of variable name
inputs
variable (str)
returns
string
'''
if len(variable) != 1:
raise Exception('len of variables inputed must be 1')
try:
return [k for k, v in locals().items() if v is variable[0]][0]
except:
return [k for k, v in globals().items() if v is variable[0]][0]
To use it in the specified question:
>>> foo = False
>>> bar = True
>>> my_dict = {get_variable_name(foo):foo,
get_variable_name(bar):bar}
>>> my_dict
{'bar': True, 'foo': False}
In reading the thread, I saw an awful lot of friction. It's easy enough to give
a bad answer, then let someone give the correct answer. Anyway, here is what I found.
From: [effbot.org] (http://effbot.org/zone/python-objects.htm#names)
The names are a bit different — they’re not really properties of the object, and the object itself doesn't know what it’s called.
An object can have any number of names, or no name at all.
Names live in namespaces (such as a module namespace, an instance namespace, a function’s local namespace).
Note: that it says the object itself doesn’t know what it’s called, so that was the clue. Python objects are not self-referential. Then it says, Names live in namespaces. We have this in TCL/TK. So maybe my answer will help (but it did help me)
jj = 123
print eval("'" + str(id(jj)) + "'")
print dir()
166707048
['__builtins__', '__doc__', '__file__', '__name__', '__package__', 'jj']
So there is 'jj' at the end of the list.
Rewrite the code as:
jj = 123
print eval("'" + str(id(jj)) + "'")
for x in dir():
print id(eval(x))
161922920
['__builtins__', '__doc__', '__file__', '__name__', '__package__', 'jj']
3077447796
136515736
3077408320
3077656800
136515736
161922920
This nasty bit of code id's the name of variable/object/whatever-you-pedantics-call-it.
So, there it is. The memory address of 'jj' is the same when we look for it directly, as when we do the dictionary look up in global name space. I'm sure you can make a function to do this. Just remember which namespace your variable/object/wypci is in.
QED.
I wrote the package sorcery to do this kind of magic robustly. You can write:
from sorcery import dict_of
my_dict = dict_of(foo, bar)
Maybe I'm overthinking this but..
str_l = next((k for k,v in locals().items() if id(l) == id(v)))
>>> bar = True
>>> foo = False
>>> my_dict=dict(bar=bar, foo=foo)
>>> next((k for k,v in locals().items() if id(bar) == id(v)))
'bar'
>>> next((k for k,v in locals().items() if id(foo) == id(v)))
'foo'
>>> next((k for k,v in locals().items() if id(my_dict) == id(v)))
'my_dict'
import re
import traceback
pattren = re.compile(r'[\W+\w+]*get_variable_name\((\w+)\)')
def get_variable_name(x):
return pattren.match( traceback.extract_stack(limit=2)[0][3]) .group(1)
a = 1
b = a
c = b
print get_variable_name(a)
print get_variable_name(b)
print get_variable_name(c)
I uploaded a solution to pypi. It's a module defining an equivalent of C#'s nameof function.
It iterates through bytecode instructions for the frame its called in, getting the names of variables/attributes passed to it. The names are found in the .argrepr of LOAD instructions following the function's name.
Most objects don't have a __name__ attribute. (Classes, functions, and modules do; any more builtin types that have one?)
What else would you expect for print(my_var.__name__) other than print("my_var")? Can you simply use the string directly?
You could "slice" a dict:
def dict_slice(D, keys, default=None):
return dict((k, D.get(k, default)) for k in keys)
print dict_slice(locals(), ["foo", "bar"])
# or use set literal syntax if you have a recent enough version:
print dict_slice(locals(), {"foo", "bar"})
Alternatively:
throw = object() # sentinel
def dict_slice(D, keys, default=throw):
def get(k):
v = D.get(k, throw)
if v is not throw:
return v
if default is throw:
raise KeyError(k)
return default
return dict((k, get(k)) for k in keys)
Well, I encountered the very same need a few days ago and had to get a variable's name which was pointing to the object itself.
And why was it so necessary?
In short I was building a plug-in for Maya. The core plug-in was built using C++ but the GUI is drawn through Python(as its not processor intensive). Since I, as yet, don't know how to return multiple values from the plug-in except the default MStatus, therefore to update a dictionary in Python I had to pass the the name of the variable, pointing to the object implementing the GUI and which contained the dictionary itself, to the plug-in and then use the MGlobal::executePythonCommand() to update the dictionary from the global scope of Maya.
To do that what I did was something like:
import time
class foo(bar):
def __init__(self):
super(foo, self).__init__()
self.time = time.time() #almost guaranteed to be unique on a single computer
def name(self):
g = globals()
for x in g:
if isinstance(g[x], type(self)):
if g[x].time == self.time:
return x
#or you could:
#return filter(None,[x if g[x].time == self.time else None for x in g if isinstance(g[x], type(self))])
#and return all keys pointing to object itself
I know that it is not the perfect solution in in the globals many keys could be pointing to the same object e.g.:
a = foo()
b = a
b.name()
>>>b
or
>>>a
and that the approach isn't thread-safe. Correct me if I am wrong.
At least this approach solved my problem by getting the name of any variable in the global scope which pointed to the object itself and pass it over to the plug-in, as argument, for it use internally.
I tried this on int (the primitive integer class) but the problem is that these primitive classes don't get bypassed (please correct the technical terminology used if its wrong). You could re-implement int and then do int = foo but a = 3 will never be an object of foo but of the primitive. To overcome that you have to a = foo(3) to get a.name() to work.
With python 2.7 and newer there is also dictionary comprehension which makes it a bit shorter. If possible I would use getattr instead eval (eval is evil) like in the top answer. Self can be any object which has the context your a looking at. It can be an object or locals=locals() etc.
{name: getattr(self, name) for name in ['some', 'vars', 'here]}
I was working on a similar problem. #S.Lott said "If you have the list of variables, what's the point of "discovering" their names?" And my answer is just to see if it could be done and if for some reason you want to sort your variables by type into lists. So anyways, in my research I came came across this thread and my solution is a bit expanded and is based on #rlotun solution. One other thing, #unutbu said, "This idea has merit, but note that if two variable names reference the same value (e.g. True), then an unintended variable name might be returned." In this exercise that was true so I dealt with it by using a list comprehension similar to this for each possibility: isClass = [i for i in isClass if i != 'item']. Without it "item" would show up in each list.
__metaclass__ = type
from types import *
class Class_1: pass
class Class_2: pass
list_1 = [1, 2, 3]
list_2 = ['dog', 'cat', 'bird']
tuple_1 = ('one', 'two', 'three')
tuple_2 = (1000, 2000, 3000)
dict_1 = {'one': 1, 'two': 2, 'three': 3}
dict_2 = {'dog': 'collie', 'cat': 'calico', 'bird': 'robin'}
x = 23
y = 29
pie = 3.14159
eee = 2.71828
house = 'single story'
cabin = 'cozy'
isClass = []; isList = []; isTuple = []; isDict = []; isInt = []; isFloat = []; isString = []; other = []
mixedDataTypes = [Class_1, list_1, tuple_1, dict_1, x, pie, house, Class_2, list_2, tuple_2, dict_2, y, eee, cabin]
print '\nMIXED_DATA_TYPES total count:', len(mixedDataTypes)
for item in mixedDataTypes:
try:
# if isinstance(item, ClassType): # use this for old class types (before 3.0)
if isinstance(item, type):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isClass.append(mapping_as_str)
isClass = [i for i in isClass if i != 'item']
elif isinstance(item, ListType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isList.append(mapping_as_str)
isList = [i for i in isList if i != 'item']
elif isinstance(item, TupleType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isTuple.append(mapping_as_str)
isTuple = [i for i in isTuple if i != 'item']
elif isinstance(item, DictType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isDict.append(mapping_as_str)
isDict = [i for i in isDict if i != 'item']
elif isinstance(item, IntType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isInt.append(mapping_as_str)
isInt = [i for i in isInt if i != 'item']
elif isinstance(item, FloatType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isFloat.append(mapping_as_str)
isFloat = [i for i in isFloat if i != 'item']
elif isinstance(item, StringType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isString.append(mapping_as_str)
isString = [i for i in isString if i != 'item']
else:
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
other.append(mapping_as_str)
other = [i for i in other if i != 'item']
except (TypeError, AttributeError), e:
print e
print '\n isClass:', len(isClass), isClass
print ' isList:', len(isList), isList
print ' isTuple:', len(isTuple), isTuple
print ' isDict:', len(isDict), isDict
print ' isInt:', len(isInt), isInt
print ' isFloat:', len(isFloat), isFloat
print 'isString:', len(isString), isString
print ' other:', len(other), other
# my output and the output I wanted
'''
MIXED_DATA_TYPES total count: 14
isClass: 2 ['Class_1', 'Class_2']
isList: 2 ['list_1', 'list_2']
isTuple: 2 ['tuple_1', 'tuple_2']
isDict: 2 ['dict_1', 'dict_2']
isInt: 2 ['x', 'y']
isFloat: 2 ['pie', 'eee']
isString: 2 ['house', 'cabin']
other: 0 []
'''
you can use easydict
>>> from easydict import EasyDict as edict
>>> d = edict({'foo':3, 'bar':{'x':1, 'y':2}})
>>> d.foo
3
>>> d.bar.x
1
>>> d = edict(foo=3)
>>> d.foo
3
another example:
>>> d = EasyDict(log=False)
>>> d.debug = True
>>> d.items()
[('debug', True), ('log', False)]
On python3, this function will get the outer most name in the stack:
import inspect
def retrieve_name(var):
"""
Gets the name of var. Does it from the out most frame inner-wards.
:param var: variable to get name from.
:return: string
"""
for fi in reversed(inspect.stack()):
names = [var_name for var_name, var_val in fi.frame.f_locals.items() if var_val is var]
if len(names) > 0:
return names[0]
It is useful anywhere on the code. Traverses the reversed stack looking for the first match.
While this is probably an awful idea, it is along the same lines as rlotun's answer but it'll return the correct result more often.
import inspect
def getVarName(getvar):
frame = inspect.currentframe()
callerLocals = frame.f_back.f_locals
for k, v in list(callerLocals.items()):
if v is getvar():
callerLocals.pop(k)
try:
getvar()
callerLocals[k] = v
except NameError:
callerLocals[k] = v
del frame
return k
del frame
You call it like this:
bar = True
foo = False
bean = False
fooName = getVarName(lambda: foo)
print(fooName) # prints "foo"
should get list then return
def get_var_name(**kwargs):
"""get variable name
get_var_name(var = var)
Returns:
[str] -- var name
"""
return list(kwargs.keys())[0]
It will not return the name of variable but you can create dictionary from global variable easily.
class CustomDict(dict):
def __add__(self, other):
return CustomDict({**self, **other})
class GlobalBase(type):
def __getattr__(cls, key):
return CustomDict({key: globals()[key]})
def __getitem__(cls, keys):
return CustomDict({key: globals()[key] for key in keys})
class G(metaclass=GlobalBase):
pass
x, y, z = 0, 1, 2
print('method 1:', G['x', 'y', 'z']) # Outcome: method 1: {'x': 0, 'y': 1, 'z': 2}
print('method 2:', G.x + G.y + G.z) # Outcome: method 2: {'x': 0, 'y': 1, 'z': 2}
With python-varname you can easily do it:
pip install python-varname
from varname import Wrapper
foo = Wrapper(True)
bar = Wrapper(False)
your_dict = {val.name: val.value for val in (foo, bar)}
print(your_dict)
# {'foo': True, 'bar': False}
Disclaimer: I'm the author of that python-varname library.
>>> a = 1
>>> b = 1
>>> id(a)
34120408
>>> id(b)
34120408
>>> a is b
True
>>> id(a) == id(b)
True
this way get varname for a maybe 'a' or 'b'.
Is there a way, lib, or something in python that I can set value in list at an index that does not exist?
Something like runtime index creation at list:
l = []
l[3] = 'foo'
# [None, None, None, 'foo']
And more further, with multi dimensional lists:
l = []
l[0][2] = 'bar'
# [[None, None, 'bar']]
Or with an existing one:
l = [['xx']]
l[0][1] = 'yy'
# [['xx', 'yy']]
There isn't a built-in, but it's easy enough to implement:
class FillList(list):
def __setitem__(self, index, value):
try:
super().__setitem__(index, value)
except IndexError:
for _ in range(index-len(self)+1):
self.append(None)
super().__setitem__(index, value)
Or, if you need to change existing vanilla lists:
def set_list(l, i, v):
try:
l[i] = v
except IndexError:
for _ in range(i-len(l)+1):
l.append(None)
l[i] = v
Not foolproof, but it seems like the easiest way to do this is to initialize a list much larger than you will need, i.e.
l = [None for i in some_large_number]
l[3] = 'foo'
# [None, None, None, 'foo', None, None None ... ]
If you really want the syntax in your question, defaultdict is probably the best way to get it:
from collections import defaultdict
def rec_dd():
return defaultdict(rec_dd)
l = rec_dd()
l[3] = 'foo'
print l
{3: 'foo'}
l = rec_dd()
l[0][2] = 'xx'
l[1][0] = 'yy'
print l
<long output because of defaultdict, but essentially)
{0: {2: 'xx'}, 1: {0: 'yy'}}
It isn't exactly a 'list of lists' but it works more or less like one.
You really need to specify the use case though... the above has some advantages (you can access indices without checking whether they exist first), and some disadvantages - for example, l[2] in a normal dict will return a KeyError, but in defaultdict it just creates a blank defaultdict, adds it, and then returns it.
Other possible implementations to support different syntactic sugars could involve custom classes etc, and will have other tradeoffs.
You cannot create a list with gaps. You could use a dict or this quick little guy:
def set_list(i,v):
l = []
x = 0
while x < i:
l.append(None)
x += 1
l.append(v)
return l
print set_list(3, 'foo')
>>> [None, None, None, 'foo']
Assuming that my list has only str and None, and I want to check assign lowered strings into another variable but if it's uppered or None, it should be rendered as None.
The code to checking for None and str.isupper() works:
for i in [None,'foo',None,'FOO',None,'bar']:
x = None if i is None or i.isupper() else i
print x
but the negated condition didn't work:
for i in [None,'foo',None,'FOO',None,'bar']:
x = i if i is not None or i.isupper() else None
print x
It returns AttributeError:
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
AttributeError: 'NoneType' object has no attribute 'isupper'
Why is that so?
Other than the ternary assignment in a loop, is there another way to perform the same operation?
You are testing if i is not None or i.isupper(). This doesn't work when i is None:
(i is not None) or (i.isupper())
is evaluated lazily; first the left is evaluated, and only if False is the second argument evaluated. The first is only False if i is None, so the right-hand expression is only ever evaluated as None.isupper().
Use and instead, and negate the isupper() test:
x = i if i is not None and not i.isupper() else None
The above expression is the proper logical inversion of i is None or i.isupper().
Alternatively use not (..) around your original expression:
x = i if not (i is None or i.isupper()) else None
Because you are using a regular for loop, there is no need to use a conditional expression here; the following, assigning to the existing loop variable i, suffices:
for i in [None,'foo',None,'FOO',None,'bar']:
if i and i.isupper():
i = None
print i
In the code that returns an AttributeError, it's because if i is none, it goes on to the second part of the or statement and checks i.isupper(), but None doesn't have an isupper() method, hence the error.
May I suggest a different approach?
items = [None,'foo',None,'FOO',None,'bar']
def splitItems(items, test):
trueItems = []
falseItems = []
for item in items:
if test(item):
trueItems.append(item)
else:
falseItems.append(item)
return trueItems, falseItems
trueItems, falseItems = splitItems(items, lambda i:i is None or i.isupper())
print "uppercase or None:", trueItems
print "lowercase:", falseItems
# uppercase or None: [None, None, 'FOO', None]
# lowercase: ['foo', 'bar']
I like #Brionius' edited answer, here is an even more general form of it, returning a dict of items from a list, keyed by the value returned by a discriminating function (could return more than just True or False).
from collections import defaultdict
def groupByEval(seq, fn):
ret = defaultdict(list)
for item in seq:
ret[fn(item)].append(item)
return dict(ret.iteritems())
test = [None,'foo',None,'FOO',None,'bar']
print groupByEval(test, lambda x: x is not None)
print groupByEval(test, lambda x: 0 if x is None else len(x))
print groupByEval(test, lambda x: x is not None and x.isupper())
print groupByEval(test, lambda x: x if x is None else sum(x.lower().count(c) for c in 'aeiou'))
Giving:
{False: [None, None, None], True: ['foo', 'FOO', 'bar']}
{0: [None, None, None], 3: ['foo', 'FOO', 'bar']}
{False: [None, 'foo', None, None, 'bar'], True: ['FOO']}
{1: ['bar'], 2: ['foo', 'FOO'], None: [None, None, None]}
Brionius' solution could then be implemented as:
def splitItems(seq, condition):
ret = groupByEval(seq, condition)
return ret.get(True,[]), ret.get(False,[])
Given a list, is there a way to get the first non-None value? And, if so, what would be the pythonic way to do so?
For example, I have:
a = objA.addreses.country.code
b = objB.country.code
c = None
d = 'CA'
In this case, if a is None, then I would like to get b. If a and b are both None, the I would like to get d.
Currently I am doing something along the lines of (((a or b) or c) or d), is there another way?
You can use next():
>>> a = [None, None, None, 1, 2, 3, 4, 5]
>>> next(item for item in a if item is not None)
1
If the list contains only Nones, it will throw StopIteration exception. If you want to have a default value in this case, do this:
>>> a = [None, None, None]
>>> next((item for item in a if item is not None), 'All are Nones')
All are Nones
I think this is the simplest way when dealing with a small set of values:
firstVal = a or b or c or d
Will always return the first non "Falsey" value which works in some cases (given you dont expect any values which could evaluate to false as #GrannyAching points out below)
first_true is an itertools recipe found in the Python 3 docs:
def first_true(iterable, default=False, pred=None):
"""Returns the first true value in the iterable.
If no true value is found, returns *default*
If *pred* is not None, returns the first item
for which pred(item) is true.
"""
# first_true([a,b,c], x) --> a or b or c or x
# first_true([a,b], x, f) --> a if f(a) else b if f(b) else x
return next(filter(pred, iterable), default)
One may choose to implement the latter recipe or import more_itertools, a library that ships with itertools recipes and more:
> pip install more_itertools
Use:
import more_itertools as mit
a = [None, None, None, 1, 2, 3, 4, 5]
mit.first_true(a, pred=lambda x: x is not None)
# 1
a = [None, None, None]
mit.first_true(a, default="All are None", pred=lambda x: x is not None)
# 'All are None'
Why use the predicate?
"First non-None" item is not the same as "first True" item, e.g. [None, None, 0] where 0 is the first non-None, but it is not the first True item. The predicate allows first_true to be useable, ensuring any first seen, non-None, falsey item in the iterable is still returned (e.g. 0, False) instead of the default.
a = [None, None, None, False]
mit.first_true(a, default="All are None", pred=lambda x: x is not None)
# 'False'
When the items in your list are expensive to calculate such as in
first_non_null = next((calculate(x) for x in my_list if calculate(x)), None)
# or, when receiving possibly None-values from a dictionary for each list item:
first_non_null = next((my_dict[x] for x in my_list if my_dict.get(x)), None)
then you might want to avoid the repetitive calculation and simplify to:
first_non_null = next(filter(bool, map(calculate, my_list)), None)
# or:
first_non_null = next(filter(bool, map(my_dict.get, my_list)), None)
Thanks to the usage of a generator expression, the calculations are only executed for the first items until a truthy value is generated.
Adapt from the following (you could one-liner it if you wanted):
values = (a, b, c, d)
not_None = (el for el in values if el is not None)
value = next(not_None, None)
This takes the first non None value, or returns None instead.
First of all want to mention that such function exists in SQL and is called coalesce. Found no such thing in Python so made up my own one, using the recipe of #alecxe.
def first_not_none(*values):
return next((v for v in values if v is not None), None)
Really helps in cases like this:
attr = 'title'
document[attr] = first_not_none(cli_args.get(attr), document_item.get(attr),
defaults_item.get(attr), '')
I would like to be able to get the name of a variable as a string but I don't know if Python has that much introspection capabilities. Something like:
>>> print(my_var.__name__)
'my_var'
I want to do that because I have a bunch of variables I'd like to turn into a dictionary like :
bar = True
foo = False
>>> my_dict = dict(bar=bar, foo=foo)
>>> print my_dict
{'foo': False, 'bar': True}
But I'd like something more automatic than that.
Python have locals() and vars(), so I guess there is a way.
As unwind said, this isn't really something you do in Python - variables are actually name mappings to objects.
However, here's one way to try and do it:
>>> a = 1
>>> for k, v in list(locals().iteritems()):
if v is a:
a_as_str = k
>>> a_as_str
a
>>> type(a_as_str)
'str'
I've wanted to do this quite a lot. This hack is very similar to rlotun's suggestion, but it's a one-liner, which is important to me:
blah = 1
blah_name = [ k for k,v in locals().iteritems() if v is blah][0]
Python 3+
blah = 1
blah_name = [ k for k,v in locals().items() if v is blah][0]
Are you trying to do this?
dict( (name,eval(name)) for name in ['some','list','of','vars'] )
Example
>>> some= 1
>>> list= 2
>>> of= 3
>>> vars= 4
>>> dict( (name,eval(name)) for name in ['some','list','of','vars'] )
{'list': 2, 'some': 1, 'vars': 4, 'of': 3}
This is a hack. It will not work on all Python implementations distributions (in particular, those that do not have traceback.extract_stack.)
import traceback
def make_dict(*expr):
(filename,line_number,function_name,text)=traceback.extract_stack()[-2]
begin=text.find('make_dict(')+len('make_dict(')
end=text.find(')',begin)
text=[name.strip() for name in text[begin:end].split(',')]
return dict(zip(text,expr))
bar=True
foo=False
print(make_dict(bar,foo))
# {'foo': False, 'bar': True}
Note that this hack is fragile:
make_dict(bar,
foo)
(calling make_dict on 2 lines) will not work.
Instead of trying to generate the dict out of the values foo and bar,
it would be much more Pythonic to generate the dict out of the string variable names 'foo' and 'bar':
dict([(name,locals()[name]) for name in ('foo','bar')])
This is not possible in Python, which really doesn't have "variables". Python has names, and there can be more than one name for the same object.
I think my problem will help illustrate why this question is useful, and it may give a bit more insight into how to answer it. I wrote a small function to do a quick inline head check on various variables in my code. Basically, it lists the variable name, data type, size, and other attributes, so I can quickly catch any mistakes I've made. The code is simple:
def details(val):
vn = val.__name__ # If such a thing existed
vs = str(val)
print("The Value of "+ str(vn) + " is " + vs)
print("The data type of " + vn + " is " + str(type(val)))
So if you have some complicated dictionary / list / tuple situation, it would be quite helpful to have the interpreter return the variable name you assigned. For instance, here is a weird dictionary:
m = 'abracadabra'
mm=[]
for n in m:
mm.append(n)
mydic = {'first':(0,1,2,3,4,5,6),'second':mm,'third':np.arange(0.,10)}
details(mydic)
The Value of mydic is {'second': ['a', 'b', 'r', 'a', 'c', 'a', 'd', 'a', 'b', 'r', 'a'], 'third': array([ 0., 1., 2., 3., 4., 5., 6., 7., 8., 9.]), 'first': [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]}
The data type of mydic is <type 'dict'>
details(mydic['first'])
The Value of mydic['first'] is (0, 1, 2, 3, 4, 5, 6)]
The data type of mydic['first'] is <type 'list'>
details(mydic.keys())
The Value of mydic.keys() is ['second', 'third', 'first']
The data type of mydic.keys() is <type 'tuple'>
details(mydic['second'][0])
The Value of mydic['second'][0] is a
The data type of mydic['second'][0] is <type 'str'>
I'm not sure if I put this in the right place, but I thought it might help. I hope it does.
I wrote a neat little useful function based on the answer to this question. I'm putting it here in case it's useful.
def what(obj, callingLocals=locals()):
"""
quick function to print name of input and value.
If not for the default-Valued callingLocals, the function would always
get the name as "obj", which is not what I want.
"""
for k, v in list(callingLocals.items()):
if v is obj:
name = k
print(name, "=", obj)
usage:
>> a = 4
>> what(a)
a = 4
>>|
I find that if you already have a specific list of values, that the way described by #S. Lotts is the best; however, the way described below works well to get all variables and Classes added throughout the code WITHOUT the need to provide variable name though you can specify them if you want. Code can be extend to exclude Classes.
import types
import math # mainly showing that you could import what you will before d
# Everything after this counts
d = dict(globals())
def kv_test(k,v):
return (k not in d and
k not in ['d','args'] and
type(v) is not types.FunctionType)
def magic_print(*args):
if len(args) == 0:
return {k:v for k,v in globals().iteritems() if kv_test(k,v)}
else:
return {k:v for k,v in magic_print().iteritems() if k in args}
if __name__ == '__main__':
foo = 1
bar = 2
baz = 3
print magic_print()
print magic_print('foo')
print magic_print('foo','bar')
Output:
{'baz': 3, 'foo': 1, 'bar': 2}
{'foo': 1}
{'foo': 1, 'bar': 2}
In python 3 this is easy
myVariable = 5
for v in locals():
if id(v) == id("myVariable"):
print(v, locals()[v])
this will print:
myVariable 5
Python3. Use inspect to capture the calling local namespace then use ideas presented here. Can return more than one answer as has been pointed out.
def varname(var):
import inspect
frame = inspect.currentframe()
var_id = id(var)
for name in frame.f_back.f_locals.keys():
try:
if id(eval(name)) == var_id:
return(name)
except:
pass
Here's the function I created to read the variable names. It's more general and can be used in different applications:
def get_variable_name(*variable):
'''gets string of variable name
inputs
variable (str)
returns
string
'''
if len(variable) != 1:
raise Exception('len of variables inputed must be 1')
try:
return [k for k, v in locals().items() if v is variable[0]][0]
except:
return [k for k, v in globals().items() if v is variable[0]][0]
To use it in the specified question:
>>> foo = False
>>> bar = True
>>> my_dict = {get_variable_name(foo):foo,
get_variable_name(bar):bar}
>>> my_dict
{'bar': True, 'foo': False}
In reading the thread, I saw an awful lot of friction. It's easy enough to give
a bad answer, then let someone give the correct answer. Anyway, here is what I found.
From: [effbot.org] (http://effbot.org/zone/python-objects.htm#names)
The names are a bit different — they’re not really properties of the object, and the object itself doesn't know what it’s called.
An object can have any number of names, or no name at all.
Names live in namespaces (such as a module namespace, an instance namespace, a function’s local namespace).
Note: that it says the object itself doesn’t know what it’s called, so that was the clue. Python objects are not self-referential. Then it says, Names live in namespaces. We have this in TCL/TK. So maybe my answer will help (but it did help me)
jj = 123
print eval("'" + str(id(jj)) + "'")
print dir()
166707048
['__builtins__', '__doc__', '__file__', '__name__', '__package__', 'jj']
So there is 'jj' at the end of the list.
Rewrite the code as:
jj = 123
print eval("'" + str(id(jj)) + "'")
for x in dir():
print id(eval(x))
161922920
['__builtins__', '__doc__', '__file__', '__name__', '__package__', 'jj']
3077447796
136515736
3077408320
3077656800
136515736
161922920
This nasty bit of code id's the name of variable/object/whatever-you-pedantics-call-it.
So, there it is. The memory address of 'jj' is the same when we look for it directly, as when we do the dictionary look up in global name space. I'm sure you can make a function to do this. Just remember which namespace your variable/object/wypci is in.
QED.
I wrote the package sorcery to do this kind of magic robustly. You can write:
from sorcery import dict_of
my_dict = dict_of(foo, bar)
Maybe I'm overthinking this but..
str_l = next((k for k,v in locals().items() if id(l) == id(v)))
>>> bar = True
>>> foo = False
>>> my_dict=dict(bar=bar, foo=foo)
>>> next((k for k,v in locals().items() if id(bar) == id(v)))
'bar'
>>> next((k for k,v in locals().items() if id(foo) == id(v)))
'foo'
>>> next((k for k,v in locals().items() if id(my_dict) == id(v)))
'my_dict'
import re
import traceback
pattren = re.compile(r'[\W+\w+]*get_variable_name\((\w+)\)')
def get_variable_name(x):
return pattren.match( traceback.extract_stack(limit=2)[0][3]) .group(1)
a = 1
b = a
c = b
print get_variable_name(a)
print get_variable_name(b)
print get_variable_name(c)
I uploaded a solution to pypi. It's a module defining an equivalent of C#'s nameof function.
It iterates through bytecode instructions for the frame its called in, getting the names of variables/attributes passed to it. The names are found in the .argrepr of LOAD instructions following the function's name.
Most objects don't have a __name__ attribute. (Classes, functions, and modules do; any more builtin types that have one?)
What else would you expect for print(my_var.__name__) other than print("my_var")? Can you simply use the string directly?
You could "slice" a dict:
def dict_slice(D, keys, default=None):
return dict((k, D.get(k, default)) for k in keys)
print dict_slice(locals(), ["foo", "bar"])
# or use set literal syntax if you have a recent enough version:
print dict_slice(locals(), {"foo", "bar"})
Alternatively:
throw = object() # sentinel
def dict_slice(D, keys, default=throw):
def get(k):
v = D.get(k, throw)
if v is not throw:
return v
if default is throw:
raise KeyError(k)
return default
return dict((k, get(k)) for k in keys)
Well, I encountered the very same need a few days ago and had to get a variable's name which was pointing to the object itself.
And why was it so necessary?
In short I was building a plug-in for Maya. The core plug-in was built using C++ but the GUI is drawn through Python(as its not processor intensive). Since I, as yet, don't know how to return multiple values from the plug-in except the default MStatus, therefore to update a dictionary in Python I had to pass the the name of the variable, pointing to the object implementing the GUI and which contained the dictionary itself, to the plug-in and then use the MGlobal::executePythonCommand() to update the dictionary from the global scope of Maya.
To do that what I did was something like:
import time
class foo(bar):
def __init__(self):
super(foo, self).__init__()
self.time = time.time() #almost guaranteed to be unique on a single computer
def name(self):
g = globals()
for x in g:
if isinstance(g[x], type(self)):
if g[x].time == self.time:
return x
#or you could:
#return filter(None,[x if g[x].time == self.time else None for x in g if isinstance(g[x], type(self))])
#and return all keys pointing to object itself
I know that it is not the perfect solution in in the globals many keys could be pointing to the same object e.g.:
a = foo()
b = a
b.name()
>>>b
or
>>>a
and that the approach isn't thread-safe. Correct me if I am wrong.
At least this approach solved my problem by getting the name of any variable in the global scope which pointed to the object itself and pass it over to the plug-in, as argument, for it use internally.
I tried this on int (the primitive integer class) but the problem is that these primitive classes don't get bypassed (please correct the technical terminology used if its wrong). You could re-implement int and then do int = foo but a = 3 will never be an object of foo but of the primitive. To overcome that you have to a = foo(3) to get a.name() to work.
With python 2.7 and newer there is also dictionary comprehension which makes it a bit shorter. If possible I would use getattr instead eval (eval is evil) like in the top answer. Self can be any object which has the context your a looking at. It can be an object or locals=locals() etc.
{name: getattr(self, name) for name in ['some', 'vars', 'here]}
I was working on a similar problem. #S.Lott said "If you have the list of variables, what's the point of "discovering" their names?" And my answer is just to see if it could be done and if for some reason you want to sort your variables by type into lists. So anyways, in my research I came came across this thread and my solution is a bit expanded and is based on #rlotun solution. One other thing, #unutbu said, "This idea has merit, but note that if two variable names reference the same value (e.g. True), then an unintended variable name might be returned." In this exercise that was true so I dealt with it by using a list comprehension similar to this for each possibility: isClass = [i for i in isClass if i != 'item']. Without it "item" would show up in each list.
__metaclass__ = type
from types import *
class Class_1: pass
class Class_2: pass
list_1 = [1, 2, 3]
list_2 = ['dog', 'cat', 'bird']
tuple_1 = ('one', 'two', 'three')
tuple_2 = (1000, 2000, 3000)
dict_1 = {'one': 1, 'two': 2, 'three': 3}
dict_2 = {'dog': 'collie', 'cat': 'calico', 'bird': 'robin'}
x = 23
y = 29
pie = 3.14159
eee = 2.71828
house = 'single story'
cabin = 'cozy'
isClass = []; isList = []; isTuple = []; isDict = []; isInt = []; isFloat = []; isString = []; other = []
mixedDataTypes = [Class_1, list_1, tuple_1, dict_1, x, pie, house, Class_2, list_2, tuple_2, dict_2, y, eee, cabin]
print '\nMIXED_DATA_TYPES total count:', len(mixedDataTypes)
for item in mixedDataTypes:
try:
# if isinstance(item, ClassType): # use this for old class types (before 3.0)
if isinstance(item, type):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isClass.append(mapping_as_str)
isClass = [i for i in isClass if i != 'item']
elif isinstance(item, ListType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isList.append(mapping_as_str)
isList = [i for i in isList if i != 'item']
elif isinstance(item, TupleType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isTuple.append(mapping_as_str)
isTuple = [i for i in isTuple if i != 'item']
elif isinstance(item, DictType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isDict.append(mapping_as_str)
isDict = [i for i in isDict if i != 'item']
elif isinstance(item, IntType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isInt.append(mapping_as_str)
isInt = [i for i in isInt if i != 'item']
elif isinstance(item, FloatType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isFloat.append(mapping_as_str)
isFloat = [i for i in isFloat if i != 'item']
elif isinstance(item, StringType):
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
isString.append(mapping_as_str)
isString = [i for i in isString if i != 'item']
else:
for k, v in list(locals().iteritems()):
if v is item:
mapping_as_str = k
other.append(mapping_as_str)
other = [i for i in other if i != 'item']
except (TypeError, AttributeError), e:
print e
print '\n isClass:', len(isClass), isClass
print ' isList:', len(isList), isList
print ' isTuple:', len(isTuple), isTuple
print ' isDict:', len(isDict), isDict
print ' isInt:', len(isInt), isInt
print ' isFloat:', len(isFloat), isFloat
print 'isString:', len(isString), isString
print ' other:', len(other), other
# my output and the output I wanted
'''
MIXED_DATA_TYPES total count: 14
isClass: 2 ['Class_1', 'Class_2']
isList: 2 ['list_1', 'list_2']
isTuple: 2 ['tuple_1', 'tuple_2']
isDict: 2 ['dict_1', 'dict_2']
isInt: 2 ['x', 'y']
isFloat: 2 ['pie', 'eee']
isString: 2 ['house', 'cabin']
other: 0 []
'''
you can use easydict
>>> from easydict import EasyDict as edict
>>> d = edict({'foo':3, 'bar':{'x':1, 'y':2}})
>>> d.foo
3
>>> d.bar.x
1
>>> d = edict(foo=3)
>>> d.foo
3
another example:
>>> d = EasyDict(log=False)
>>> d.debug = True
>>> d.items()
[('debug', True), ('log', False)]
On python3, this function will get the outer most name in the stack:
import inspect
def retrieve_name(var):
"""
Gets the name of var. Does it from the out most frame inner-wards.
:param var: variable to get name from.
:return: string
"""
for fi in reversed(inspect.stack()):
names = [var_name for var_name, var_val in fi.frame.f_locals.items() if var_val is var]
if len(names) > 0:
return names[0]
It is useful anywhere on the code. Traverses the reversed stack looking for the first match.
While this is probably an awful idea, it is along the same lines as rlotun's answer but it'll return the correct result more often.
import inspect
def getVarName(getvar):
frame = inspect.currentframe()
callerLocals = frame.f_back.f_locals
for k, v in list(callerLocals.items()):
if v is getvar():
callerLocals.pop(k)
try:
getvar()
callerLocals[k] = v
except NameError:
callerLocals[k] = v
del frame
return k
del frame
You call it like this:
bar = True
foo = False
bean = False
fooName = getVarName(lambda: foo)
print(fooName) # prints "foo"
should get list then return
def get_var_name(**kwargs):
"""get variable name
get_var_name(var = var)
Returns:
[str] -- var name
"""
return list(kwargs.keys())[0]
It will not return the name of variable but you can create dictionary from global variable easily.
class CustomDict(dict):
def __add__(self, other):
return CustomDict({**self, **other})
class GlobalBase(type):
def __getattr__(cls, key):
return CustomDict({key: globals()[key]})
def __getitem__(cls, keys):
return CustomDict({key: globals()[key] for key in keys})
class G(metaclass=GlobalBase):
pass
x, y, z = 0, 1, 2
print('method 1:', G['x', 'y', 'z']) # Outcome: method 1: {'x': 0, 'y': 1, 'z': 2}
print('method 2:', G.x + G.y + G.z) # Outcome: method 2: {'x': 0, 'y': 1, 'z': 2}
With python-varname you can easily do it:
pip install python-varname
from varname import Wrapper
foo = Wrapper(True)
bar = Wrapper(False)
your_dict = {val.name: val.value for val in (foo, bar)}
print(your_dict)
# {'foo': True, 'bar': False}
Disclaimer: I'm the author of that python-varname library.
>>> a = 1
>>> b = 1
>>> id(a)
34120408
>>> id(b)
34120408
>>> a is b
True
>>> id(a) == id(b)
True
this way get varname for a maybe 'a' or 'b'.