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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
def move(self):
z = self.comboBox.currentText()
print(z)
Hospital = newtest.my_function()
i = Hospital.index(z)
print('The index of :', i)
user = newuser.my_function()
global (user[i])
print (user[i])
return user[i]
def my_doc():
url = 'https://test.com/steth/get-list'
myobj = {'mongoId': 'user[i]'}
x = requests.post(url, data = myobj)
y=x.json();
print(y)
my_doc()
I need to get user[i] in the second function my_doc.so i made user[i] global.But it is showing syntax error as
global (user[i])
^
SyntaxError: invalid syn
Just get the return of one function, and input it into the other.
class Obj:
def func1(self):
return "something"
# Assuming func2 is inside class.
def func2_class(self, something):
print(something)
# Assuming func2 is outside class.
def func2(something):
print(something)
obj = Obj()
something = obj.func1()
func2(something) # Outside class.
obj.func2(something) # Inside class.
I have a text file a.txt. I want to perform some preprocess on it like remove punct. and split it into words.
I have written the following code to perform few operations.
class pre:
def __init__(self,textfilepath):
self.textfilepath = textfilepath
def __str__(self,textfilepath):
return str(textfilepath)
def process(textpathfile):
with open(textpathfile, r) as abc:
a = abc.translate(string.maketrans("",""), string.punctuation)
a = a.split(' ')
return a
pre("a.txt")
I tried executing it.But it gave an error pre doesn't take arguments. Can any one help me with how to do this? Thanks all.
You shouldn't pass arguments to __str__. Instead you can access them through the properties of self:
class pre:
def __init__(self,textfilepath):
self.textfilepath = textfilepath
def __str__(self):
return self.textfilepath
def process(self):
with open(self.textfilepath, r) as abc:
a = abc.translate(string.maketrans("",""), string.punctuation)
a = a.split(' ')
return a
p = pre("a.txt")
print(p)
filedata = p.process()
print(filedata)
I have these two functions:
def check_channel_number(self):
print "***************Channel Checker *********************"
print ''
user_channel_number = int(re.sub('\D', '', raw_input("Enter a channel number, (3digit): "))[:3]);
channel = ("channelNr= '%d'") % (user_channel_number)
print channel
# channel_search = channel + str(user_channel_number)
datafile = file('output.txt')
found = False
for line in datafile:
if channel in line:
found = True
print 'The channel number you entered is correct and will be deleted'
return user_channel_number
print 'The channel number you entered is not on the planner'
return False
and
def delete_events(self):
if user_channel_number == True:
return 'The program number is correct and will be deleted'
# action = 'DeleteEvent'
menu_action = 'all'
book = 'RECYC:687869882'
arg_list = [('C:\\Users\\yke01\\Documents\\StormTest\\Scripts\\Completed'
'\\Utils\\UPNP_Client_Cmd_Line.py')]
arg_list.append(' --action=')
arg_list.append(action)
arg_list.append(' --ip=')
arg_list.append('10.10.8.89')
arg_list.append(' --objectId=')
arg_list.append(book)
subprocess.call(["python", arg_list])
print 'The program deleted successfully'
When I run my script, it says that user_channel_number is not defined globally. How can I use user_channel_number inside the delete_events function?
When you define a variable inside of a function, it is a local variable, meaning that it can only be accessed within that function.
Within a Class
It looks like you're inside a class, so you can make the variable accessible to all methods in the class by defining it like this:
def check_channel_number(self):
self.user_channel_number = ...
And then in your second function, you can use it like the following:
def delete_events(self):
if self.user_channel_number:
Outside of a class
If you aren't using methods inside of a class, you can instead use the global builtin.
For example,
def check_channel_number():
global user_channel_number
user_channel_number = ...
def delete_events():
if user_channel_number:
...
Using a value returned from a function
Instead in your first function, check_channel_number(), you can have it return user_channel_number. You can then call that function inside of delete_events(), like the following:
def check_channel_number():
user_channel_number = ...
return user_channel_number
def delete_events():
if check_channel_number():
...
Functions can not share their local variables. You can return the value from the first and pass it to the second:
def check_channel_number(self):
...
return user_channel_number
def delete_events(self):
user_channel_number = self.check_channel_number()
...
Or save value on the object:
def check_channel_number(self):
...
self.user_channel_number = user_channel_number
...
def delete_events(self):
if self.user_channel_number:
....
So I think when you call the check_channel_number function, user_channel_number is defined in there, so when you call delete_events, it has gone out of scope, maybe something like this would help?
user_channel_number = check_channel_number()
delete_events()
I'd probably have the user_channel_number as an input to the delete function too, so it would turn into this: (where ucn is the user_channel_number)
def delete_events(self, ucn):
if ucn == True:
print 'The program number is correct and will be deleted'
# action = 'DeleteEvent'
menu_action = 'all'
book = 'RECYC:687869882'
arg_list = [('C:\\Users\\yke01\\Documents\\StormTest\\Scripts\\Completed'
'\\Utils\\UPNP_Client_Cmd_Line.py')]
arg_list.append(' --action=')
arg_list.append(action)
arg_list.append(' --ip=')
arg_list.append('10.10.8.89')
arg_list.append(' --objectId=')
arg_list.append(book)
subprocess.call(["python", arg_list])
print 'The program deleted successfully'
I have also changed `return 'The program number is correct and will be deleted'' to a print statement as I have a feeling the return would end the function before the other lines of code would be run
So the code would probably end up being something like:
user_channel_number = check_channel_number()
delete_events(user_channel_number)
EDIT:
just noticed it looks like your functions are part of a class,
in that case, you could do:
self.ucn = self.check_channel_number()
self.delete_events(self.ucn)
(or if you dont want to pass the user_channel_number into the function you could change if user_channel_number: to if self. user_channel_number:
I want to change the function name according to result obtained from another function but the function definition remains same How can i do this i tried the following example but it didn't work
def f(text):
def x(text):
return text+"example"
name=x(text)
def name(y):
return y
return name
p=f("hi ")
print p("hello")
print p.__name__
OUTPUT
hello
name
But i want the function name p.__name__ as "hi example" not name
You can simply assign to __name__:
def f(text):
def r(y):
return y
r.__name__ = text + "example"
return r
p = f("hi ")
print (p("hello")) # Outputs "hello"
print (p.__name__) # Outputs "hi example"
Note that a function name does not have any influence on the function's behavior though, and does not have any meaning except as a part of the string representation or a debugging aid.