How to get the original variable name of variable passed to a function [duplicate]

This question already has answers here: Getting the name of a variable as a string (31 answers) Closed 2 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 开发者_开发技巧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