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Getting the name of a variable as a string
(32 answers)
Closed 4 months ago.
Is it possible to get the original variable name of a variable passed to a function? E.g.
foobar = "foo"
def func(var):
print var.origname
So that:
func(foobar)
Returns:
>>foobar
EDIT:
All I was trying to do was make a function like:
def log(soup):
f = open(varname+'.html', 'w')
print >>f, soup.prettify()
f.close()
.. and have the function generate the filename from the name of the variable passed to it.
I suppose if it's not possible I'll just have to pass the variable and the variable's name as a string each time.
EDIT: To make it clear, I don't recommend using this AT ALL, it will break, it's a mess, it won't help you in any way, but it's doable for entertainment/education purposes.
You can hack around with the inspect module, I don't recommend that, but you can do it...
import inspect
def foo(a, f, b):
frame = inspect.currentframe()
frame = inspect.getouterframes(frame)[1]
string = inspect.getframeinfo(frame[0]).code_context[0].strip()
args = string[string.find('(') + 1:-1].split(',')
names = []
for i in args:
if i.find('=') != -1:
names.append(i.split('=')[1].strip())
else:
names.append(i)
print names
def main():
e = 1
c = 2
foo(e, 1000, b = c)
main()
Output:
['e', '1000', 'c']
To add to Michael Mrozek's answer, you can extract the exact parameters versus the full code by:
import re
import traceback
def func(var):
stack = traceback.extract_stack()
filename, lineno, function_name, code = stack[-2]
vars_name = re.compile(r'\((.*?)\).*$').search(code).groups()[0]
print vars_name
return
foobar = "foo"
func(foobar)
# PRINTS: foobar
Looks like Ivo beat me to inspect, but here's another implementation:
import inspect
def varName(var):
lcls = inspect.stack()[2][0].f_locals
for name in lcls:
if id(var) == id(lcls[name]):
return name
return None
def foo(x=None):
lcl='not me'
return varName(x)
def bar():
lcl = 'hi'
return foo(lcl)
bar()
# 'lcl'
Of course, it can be fooled:
def baz():
lcl = 'hi'
x='hi'
return foo(lcl)
baz()
# 'x'
Moral: don't do it.
Another way you can try if you know what the calling code will look like is to use traceback:
def func(var):
stack = traceback.extract_stack()
filename, lineno, function_name, code = stack[-2]
code will contain the line of code that was used to call func (in your example, it would be the string func(foobar)). You can parse that to pull out the argument
You can't. It's evaluated before being passed to the function. All you can do is pass it as a string.
#Ivo Wetzel's answer works in the case of function call are made in one line, like
e = 1 + 7
c = 3
foo(e, 100, b=c)
In case that function call is not in one line, like:
e = 1 + 7
c = 3
foo(e,
1000,
b = c)
below code works:
import inspect, ast
def foo(a, f, b):
frame = inspect.currentframe()
frame = inspect.getouterframes(frame)[1]
string = inspect.findsource(frame[0])[0]
nodes = ast.parse(''.join(string))
i_expr = -1
for (i, node) in enumerate(nodes.body):
if hasattr(node, 'value') and isinstance(node.value, ast.Call)
and hasattr(node.value.func, 'id') and node.value.func.id == 'foo' # Here goes name of the function:
i_expr = i
break
i_expr_next = min(i_expr + 1, len(nodes.body)-1)
lineno_start = nodes.body[i_expr].lineno
lineno_end = nodes.body[i_expr_next].lineno if i_expr_next != i_expr else len(string)
str_func_call = ''.join([i.strip() for i in string[lineno_start - 1: lineno_end]])
params = str_func_call[str_func_call.find('(') + 1:-1].split(',')
print(params)
You will get:
[u'e', u'1000', u'b = c']
But still, this might break.
You can use python-varname package
from varname import nameof
s = 'Hey!'
print (nameof(s))
Output:
s
Package below:
https://github.com/pwwang/python-varname
For posterity, here's some code I wrote for this task, in general I think there is a missing module in Python to give everyone nice and robust inspection of the caller environment. Similar to what rlang eval framework provides for R.
import re, inspect, ast
#Convoluted frame stack walk and source scrape to get what the calling statement to a function looked like.
#Specifically return the name of the variable passed as parameter found at position pos in the parameter list.
def _caller_param_name(pos):
#The parameter name to return
param = None
#Get the frame object for this function call
thisframe = inspect.currentframe()
try:
#Get the parent calling frames details
frames = inspect.getouterframes(thisframe)
#Function this function was just called from that we wish to find the calling parameter name for
function = frames[1][3]
#Get all the details of where the calling statement was
frame,filename,line_number,function_name,source,source_index = frames[2]
#Read in the source file in the parent calling frame upto where the call was made
with open(filename) as source_file:
head=[source_file.next() for x in xrange(line_number)]
source_file.close()
#Build all lines of the calling statement, this deals with when a function is called with parameters listed on each line
lines = []
#Compile a regex for matching the start of the function being called
regex = re.compile(r'\.?\s*%s\s*\(' % (function))
#Work backwards from the parent calling frame line number until we see the start of the calling statement (usually the same line!!!)
for line in reversed(head):
lines.append(line.strip())
if re.search(regex, line):
break
#Put the lines we have groked back into sourcefile order rather than reverse order
lines.reverse()
#Join all the lines that were part of the calling statement
call = "".join(lines)
#Grab the parameter list from the calling statement for the function we were called from
match = re.search('\.?\s*%s\s*\((.*)\)' % (function), call)
paramlist = match.group(1)
#If the function was called with no parameters raise an exception
if paramlist == "":
raise LookupError("Function called with no parameters.")
#Use the Python abstract syntax tree parser to create a parsed form of the function parameter list 'Name' nodes are variable names
parameter = ast.parse(paramlist).body[0].value
#If there were multiple parameters get the positional requested
if type(parameter).__name__ == 'Tuple':
#If we asked for a parameter outside of what was passed complain
if pos >= len(parameter.elts):
raise LookupError("The function call did not have a parameter at postion %s" % pos)
parameter = parameter.elts[pos]
#If there was only a single parameter and another was requested raise an exception
elif pos != 0:
raise LookupError("There was only a single calling parameter found. Parameter indices start at 0.")
#If the parameter was the name of a variable we can use it otherwise pass back None
if type(parameter).__name__ == 'Name':
param = parameter.id
finally:
#Remove the frame reference to prevent cyclic references screwing the garbage collector
del thisframe
#Return the parameter name we found
return param
If you want a Key Value Pair relationship, maybe using a Dictionary would be better?
...or if you're trying to create some auto-documentation from your code, perhaps something like Doxygen (http://www.doxygen.nl/) could do the job for you?
I wondered how IceCream solves this problem. So I looked into the source code and came up with the following (slightly simplified) solution. It might not be 100% bullet-proof (e.g. I dropped get_text_with_indentation and I assume exactly one function argument), but it works well for different test cases. It does not need to parse source code itself, so it should be more robust and simpler than previous solutions.
#!/usr/bin/env python3
import inspect
from executing import Source
def func(var):
callFrame = inspect.currentframe().f_back
callNode = Source.executing(callFrame).node
source = Source.for_frame(callFrame)
expression = source.asttokens().get_text(callNode.args[0])
print(expression, '=', var)
i = 1
f = 2.0
dct = {'key': 'value'}
obj = type('', (), {'value': 42})
func(i)
func(f)
func(s)
func(dct['key'])
func(obj.value)
Output:
i = 1
f = 2.0
s = string
dct['key'] = value
obj.value = 42
Update: If you want to move the "magic" into a separate function, you simply have to go one frame further back with an additional f_back.
def get_name_of_argument():
callFrame = inspect.currentframe().f_back.f_back
callNode = Source.executing(callFrame).node
source = Source.for_frame(callFrame)
return source.asttokens().get_text(callNode.args[0])
def func(var):
print(get_name_of_argument(), '=', var)
If you want to get the caller params as in #Matt Oates answer answer without using the source file (ie from Jupyter Notebook), this code (combined from #Aeon answer) will do the trick (at least in some simple cases):
def get_caller_params():
# get the frame object for this function call
thisframe = inspect.currentframe()
# get the parent calling frames details
frames = inspect.getouterframes(thisframe)
# frame 0 is the frame of this function
# frame 1 is the frame of the caller function (the one we want to inspect)
# frame 2 is the frame of the code that calls the caller
caller_function_name = frames[1][3]
code_that_calls_caller = inspect.findsource(frames[2][0])[0]
# parse code to get nodes of abstract syntact tree of the call
nodes = ast.parse(''.join(code_that_calls_caller))
# find the node that calls the function
i_expr = -1
for (i, node) in enumerate(nodes.body):
if _node_is_our_function_call(node, caller_function_name):
i_expr = i
break
# line with the call start
idx_start = nodes.body[i_expr].lineno - 1
# line with the end of the call
if i_expr < len(nodes.body) - 1:
# next expression marks the end of the call
idx_end = nodes.body[i_expr + 1].lineno - 1
else:
# end of the source marks the end of the call
idx_end = len(code_that_calls_caller)
call_lines = code_that_calls_caller[idx_start:idx_end]
str_func_call = ''.join([line.strip() for line in call_lines])
str_call_params = str_func_call[str_func_call.find('(') + 1:-1]
params = [p.strip() for p in str_call_params.split(',')]
return params
def _node_is_our_function_call(node, our_function_name):
node_is_call = hasattr(node, 'value') and isinstance(node.value, ast.Call)
if not node_is_call:
return False
function_name_correct = hasattr(node.value.func, 'id') and node.value.func.id == our_function_name
return function_name_correct
You can then run it as this:
def test(*par_values):
par_names = get_caller_params()
for name, val in zip(par_names, par_values):
print(name, val)
a = 1
b = 2
string = 'text'
test(a, b,
string
)
to get the desired output:
a 1
b 2
string text
Since you can have multiple variables with the same content, instead of passing the variable (content), it might be safer (and will be simpler) to pass it's name in a string and get the variable content from the locals dictionary in the callers stack frame. :
def displayvar(name):
import sys
return name+" = "+repr(sys._getframe(1).f_locals[name])
If it just so happens that the variable is a callable (function), it will have a __name__ property.
E.g. a wrapper to log the execution time of a function:
def time_it(func, *args, **kwargs):
start = perf_counter()
result = func(*args, **kwargs)
duration = perf_counter() - start
print(f'{func.__name__} ran in {duration * 1000}ms')
return result
Currently in my code i am just copy and pasting blocks of code like these 20+ times, i need some help on how to make this into a function to save space
if chosenrace == "Var Human":
randclass = random.choice(varhumanclasses)
if chosenrace == "Aasimar":
randclass = random.choice(aasimarclasses)
if chosenrace == "Aarakocra":
randclass = random.choice(aarakocraclasses)
if chosenrace == "Warforged":
randclass = random.choice(warforgedclasses)
A possible solution would be to have create a dictionary linking the strings, to the variables. For example,
class_dict = {
"Var Human": varhumanclasses,
"Aasimar": aasimarclasses
}
Then, you could create a function that takes the chosen race string and returns a random choice using the correct class variable from the dictionary.
def random_class(race):
return random.choice(class_dict[race])
like this
def pick(chosenrace): return random.choice({
"Var Human" : varhumanclasses,
"Aasimar" : aasimarclasses,
"Aarakocra" : aarakocraclasses,
"Warforged" : warforgedclasses,
}.get(chosenrace, notfoundclasses))
I liked and up-voted the solution by #tintins7a6164. If you don't want to maintain a dictionary, you can consider the snippet below. It assumes that varhumanclasses etc are declared on the global scope.
import random
varhumanclasses = [1, 2, 3]
aasimarclasses = [5, 6, 7]
def get_classes_from_race(race: str):
classes_s = race.lower().replace(" ", "") + "classes"
if classes_s in globals():
f = globals()[classes_s]
else:
raise ValueError(f"{classes_s} not found")
if not isinstance(f, list):
raise ValueError(f"{classes_s} is not declared as a function")
return f
print(random.choice(get_classes_from_race("Var Human")))
print(random.choice(get_classes_from_race("Aasimar")))
Given that you have an empty dictionary
data = {}
I have a path and a value
path = "root.sub.item"
value = 12
How could I recursively add objects that do not exist?
def add_value(path, value):
for part in path.split('.'):
if not part in data:
data[part] = {}
The expected output for this would be:
data = {
'root':{
'sub':{
'item': 12
}
}
}
Could somebody help out with this or point me in the right direction?
I'm using Python 3.6.
You can use some another kind of solution like recursive defaultdict, as in this answer.
A quick and stupid example about how it can used:
from collections import defaultdict
def func(rdict, path, value):
items = path.split('.')
d = rdict[items[0]]
for item in items[1:-1]:
d = d[item]
d[items[-1]] = value
nested_dict = lambda: defaultdict(nested_dict)
result = nested_dict()
func(result, 'root.sub.item', 12)
func(result, 'root.moon.value', 1)
assert result['root']['sub']['item'] == 12
assert result['root']['moon']['value'] == 1
assert result['root']['moon']['noop'] != 0
You're almost there, you just need to keep track of how far you are into the tree structure, and a way to know when you're on the last element of the path:
def add_value(path, value):
tmp = data
parts = list(path.split('.'))
for i in range(len(parts) - 1):
part = parts[i]
if not part in tmp:
tmp[part] = {}
tmp = tmp[part]
tmp[parts[-1]] = value
you can try Raymond Hettinger recipe :
source: https://twitter.com/raymondh/status/343823801278140417
from collections import defaultdict
infinity_dict=lambda:defaultdict(infinity_dict)
d=infinity_dict()
d['root']['sub']['item'] = 12
I am importing the fun.py module into the chr_cnt function. The cnt_list function takes a list as argument. When I call this function in chr_cnt function using import, I am not sure how to pass an argument for the chr_cnt function to the cnt_list function.
My fun.py module:
def cnt_list(li):
my_dict = {}
for i in li:
if i in my_dict:
my_dict[i] = my_dict[i]+1
else:
my_dict[i] = 1
return my_dict
# print cnt_list([1,2,3,3,1])
My script:
import fun
def chr_cnt(s):
res={}
res=fun.cnt_list(s) # or res=fun.cnt_list(list(s))
return res
print chr_cnt("aabbc")
expected result:
{'a':2, 'b':2,'c':1}
This works fine for me? Are you sure you have the right indenting? I've made it a bit shorter for you:
fun.py:
def cnt_list(li):
my_dict = {}
for i in li:
if i in my_dict:
my_dict[i] = my_dict[i]+1
else:
my_dict[i] = 1
return my_dict
main.py:
import fun
def chr_cnt(s):
return fun.cnt_list(s)
print chr_cnt("aabbc")
I want to dynamically add values in a nested dictionary. I am trying to cache similarity score of two words with their part-of-speech-tag.
In short I want to store values as this;
synset_cache[word1][word1_tag][word2][word2_tag] = score
class MyClass(Object):
def __init__(self):
MyClass.synset_cache={} #dict
def set_cache(self,word1, word1_tag, word2, word2_tag, score)
try:
MyClass.synset_cache[word1]
except:
MyClass.synset_cache[word1]={} #create new dict
try:
MyClass.synset_cache[word1][word1_tag]
except:
MyClass.synset_cache[word1][word1_tag]={} #create new dict
try:
MyClass.synset_cache[word1][word1_tag][word2]
except:
MyClass.synset_cache[word1][word1_tag][word2]={} #create new dict
#store the value
MyClass.synset_cache[word1][word1_tag][word2][word2_tag] = score
But I am getting this error.
Type error: list indices must be integers, not unicode
Line number it shows is at MyClass.synset_cache[word1][word1_tag]={} #create new dict.
How can I get this working?
EDIT:
According to the #Robᵩ's comments on his answer; I was assigning a list to this MyClass.synset_cache in another method(note it is at the class-level). So this code part had no errors.
Use dict.setdefault.
This might work:
#UNTESTED
d = MyClass.synset_cache.setdefault(word1, {})
d = d.setdefault(word1_tag, {})
d = d.setdefault(word2, {})
d[word2_tag] = score
Alternatively, you can use this handy recursive defaultdict that springs up new levels of dict automatically. (See: here and here.)
import collections
def tree():
return collections.defaultdict(tree)
class MyClass(Object):
def __init__(self):
MyClass.synset_cache=tree()
def set_cache(self,word1, word1_tag, word2, word2_tag, score)
MyClass.synset_cache[word1][word1_tag][word2][word2_tag] = score
This will be data dependent, as at least for some test data (see below), the code does not produce that error. How are you calling it?
Also, note that as written above, it won't compile due to some syntax errors (i.e. no colon to end the def set_cache line).
Below is some tweaked-to-compile code with some example calling data and how that pretty-prints:
#!/usr/bin/env python
import pprint
class MyClass():
def __init__(self):
MyClass.synset_cache={} #dict
def set_cache(self,word1, word1_tag, word2, word2_tag, score):
try:
MyClass.synset_cache[word1]
except:
MyClass.synset_cache[word1]={} #create new dict
try:
MyClass.synset_cache[word1][word1_tag]
except:
MyClass.synset_cache[word1][word1_tag]={} #create new dict
try:
MyClass.synset_cache[word1][word1_tag][word2]
except:
MyClass.synset_cache[word1][word1_tag][word2]={} #create new dict
#store the value
MyClass.synset_cache[word1][word1_tag][word2][word2_tag] = score
x = MyClass()
x.set_cache('foo', 'foo-tag', 'bar', 'bar-tag', 100)
pp = pprint.PrettyPrinter(indent=4)
pp.pprint(x.synset_cache)
Which outputs:
{ 'foo': { 'foo-tag': { 'bar': { 'bar-tag': 100}}}}
A couple other things of note...
I'd recommend using the in style syntax to check for key presence rather than try-except. It's more compact and more Pythonic.
Also, your main variable, synset_cache, is class-level (i.e. static). Did you mean for that to be the case?