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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 state_from_record(state_name):
state_split = state_name.split(",")
return state_split
def cases_from_record(covid_cases):
covid_split = covid_cases.split(",")
return covid_split
def deaths_from_record(covid_deaths):
death_split = covid_deaths.split(",")
return death_split
result1 = state_from_record(result[0])
print(result1)
This is the second part of the code which continues on:
import random
def state_report(state, data_list):
if state_split is random:
states = choice(state_split)
for s in states:
if states == state_split:
return states + "\n" + "Total Confirmed Cases: " + covid_split + "Total Deaths: " + death_split
else:
return "No record found for " + states
result2 = state_report(states, state_split)
print(result2)
I am trying to use a previous code and it keeps on coming as a name error saying that "states" doesn't exist.
here is my output:
NameError Traceback (most recent call last)
<ipython-input-20-8fee8f642c90> in <module>()
10 return "No record found for " + states
11
---> 12 result2 = state_report(states, state_split)
13 print(result2)
NameError: name 'states' is not defined
What you are bumping into is a programming concept called the scope
Imagine these two functions:
def first_func():
foo = "abc"
print(foo)
def second_func():
print(foo)
second_func()
Running this code will raise NameError, because variable foo is out of the scope of the second_func, since it is defined within the boundaries of the first_func.
If you move the variable foo out of the first function, like so:
foo = "abc"
def first_func():
print(foo)
def second_func():
print(foo)
second_func()
Both functions will run fine. Because variable foo is now defined in a broader scope and accessible from within both functions.
The function menu5 returns a message to the user. I would like at the same time that the user called this function, that it called another similar function, that sent message to another person.
Here is the code:
def menu5(self, message=None, match=None, to=None):
# Retransfer the requester's phone
number = message.getFrom()
# Cut after the #
number = number.split('#')
# Separate only the number
number = number[0]
# Delete the 55
number = number[2:13]
# Person who will receive the message
toSend = '5527999999999#s.whatsapp.net'
# Function call to be triggered
self.operator(msg=number, op=toSend)
return textMessageProtocolEntity(txtMenu5, to=message.getFrom())
def operator(self, to=None, msg=None, op=None):
return TextMessageProtocolEntity(msg, to=op)
If you want the return value of some function, you need to explicitly store it:
def menu5(self, message=None, match=None, to=None):
# ...
# Function call to be triggered
txtmsg = self.operator(msg=number, op=toSend)
return TextMessageProtocolEntity(txtMenu5, to=message.getFrom()), txtmsg
The function menu5 now returns a two-element tuple with two TextMessageProtocolEntitys in it. Note that your original code was always calling self.operator, as expected - it just wasn't doing anything with the return value.
for x in non_neutral.collect():
tweet = str(x[2])
sid = x[1]
status = x[0]
text = word_tokenize(tweet)
text1 = list(text)
tweet = x[2].split()
pronoun = intersect(second_pronoun,tweet)
perojective = intersect(less_offensive,tweet)
if pronoun:
pronoun_index = tweet.index(pronoun[0])
pero_index = tweet.index(perojective[0])
if pero_index <= pronoun_index+3:
status = 1
return Row(status=status,tid=sid,tweet = str(tweet))
else:
status = 0
return Row(status=status,tid=sid,tweet = str(tweet))
For this particular snippet of code I am constantly getting this error and I don't understand why
File "<ipython-input-5-0484b7e6e4fa>", line 15
return Row(status=status,tid=sid,tweet = str(tweet))
SyntaxError: 'return' outside function
I have tried writing the code again but still getting the same error.
your program doesn't actually contain a function. Return statements must be contained within a function, you haven't defined any in this case.
Try something more like the following (note that this doesn't include all of your code it is just an example):
def Foo():
#Here is where you put all of your code
#Since it is now in a function a value can be returned from it
if pronoun:
pronoun_index = tweet.index(pronoun[0])
pero_index = tweet.index(perojective[0])
if pero_index <= pronoun_index+3:
status = 1
return Row(status=status,tid=sid,tweet = str(tweet))
else:
status = 0
return Row(status=status,tid=sid,tweet = str(tweet))
Foo()
So long as you put your code in a function it will work. The syntax for a basic function definition in python is: def Foo(Bar): Where Foo is the name of the function and Bar is any parameters you may need, each separated by a comma.
I don't see the keyword def in your code snippet, which would indicate the beginning of a function definition. Is the snippet taken from the body of a function?
Here is a working sample of return in a for loop:
from random import shuffle
def loop_return():
values = [0,1]
shuffle(values)
for i in values:
if i == 0:
return 'Zero first.'
if i == 1:
return 'One first.'
You don't actually have a function, so you can't return anything. You could fix it by making the code a procedure.
I want to create a separate file class that will be a print function. So I want it to print out a list when it gets the parameter. So lets call the class print_list and let's take the start variable I want the function to go through the list and print out the data. How do I create this function?
from print_list import *
class node:
pass
start = node
point = start
point.data= 1
print (point.data )
point.next = node ()
point = point.next
point.data= 2
print (point.data )
point.next = node ()
point = point.next
point.data= 3
print (point.data )
point.next = node ()
point = point.next
point.data= 4
print (point.data )
point.next = None
point = point.next
Why not try the build in print function of python? Something like
print(x)
or, if x is an iterable like a list, you could also do
print(*x)