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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
I want to be able to mock a function that mutates an argument, and that it's mutation is relevant in order for the code to continue executing correctly.
Consider the following code:
def mutate_my_dict(mutable_dict):
if os.path.exists("a.txt"):
mutable_dict["new_key"] = "new_value"
return True
def function_under_test():
my_dict = {"key": "value"}
if mutate_my_dict(my_dict):
return my_dict["new_key"]
return "No Key"
def test_function_under_test():
with patch("stack_over_flow.mutate_my_dict") as mutate_my_dict_mock:
mutate_my_dict_mock.return_value = True
result = function_under_test()
assert result == "new_value"
**Please understand i know i can just mock os.path.exists in this case but this is just an example. I intentionally want to mock the function and not the external module.
**
I also read the docs here:
https://docs.python.org/3/library/unittest.mock-examples.html#coping-with-mutable-arguments
But it doesn't seem to fit in my case.
This is the test i've written so far, but it obviously doesn't work since the key changes:
def test_function_under_test():
with patch("stack_over_flow.mutate_my_dict") as mutate_my_dict_mock:
mutate_my_dict_mock.return_value = True
result = function_under_test()
assert result == "new_value"
Thanks in advance for all of your time :)
With the help of Peter i managed to come up with this final test:
def mock_mutate_my_dict(my_dict):
my_dict["new_key"] = "new_value"
return True
def test_function_under_test():
with patch("stack_over_flow.mutate_my_dict") as mutate_my_dict_mock:
mutate_my_dict_mock.side_effect = mock_mutate_my_dict
result = function_under_test()
assert result == "new_value"
How it works is that with a side effect you can run a function instead of the intended function.
In this function you need to both change all of the mutating arguments and return the value returned.
A very similar question was asked, however it doesn't answer my doubt.
#mock.patch('myget.myvalue.myfrom.myAPI')
def test_thatdoesntwork(myAPI_mock):
orig_function = myget.myvalue.myfrom.myAPI
nth_value = get_valuefrom_myDB(n=111)
def mock_function_for_nth_value_only(myvalue):
if myvalue == nth_value:
return get_valuefrom_myDB(n+1)
else:
return orig_function(n)
nplus1th_value = get_valuefrom_myDB(n=112)
myvalue = myget.myvalue.myfrom.myAPI(nplus1th_value)
# getting "CRITICAL: maximum recursion level exceeded"
am assuming when I call orig_function , I am actually calling the mocked function, and that causes the CRITICAL recursion error....
but what am I doing wrong?
Thanks!!
The #mock.patch decorator replaces the function before your code starts, so orig_function = myget.myvalue.myfrom.myAPI already points to the mocked version.
Instead, you can use the context manager to ensure that you only replace the function in the scope you want.
This test version should work better for you:
def test_that_works():
orig_function = myget.myvalue.myfrom.myAPI
nth_value = get_valuefrom_myDB(n=111)
def mock_function_for_nth_value_only(myvalue):
if myvalue == nth_value:
return get_valuefrom_myDB(myvalue + 1)
else:
return orig_function(myvalue)
with mock.patch('myget.myvalue.myfrom.myAPI',
side_effect=mock_function_for_nth_value_only):
nplus1th_value = get_valuefrom_myDB(n=112)
myvalue = myget.myvalue.myfrom.myAPI(nplus1th_value)
I have a main function, and helper functions inside the main function that will retrieve values from an excel spreadsheet
Ex.
import openpyxl
def main():
dict = {}
dname = 'Animal list'
animal = {}
while opt in ['0', '1']:
if opt == '0':
print('goodbye')
if opt == '1':
file_open(dname, dict, animal)
return
def file_open(dname, dict, animal):
open_excel(dname)
create_animal_dict(data, dict)
def open_excel(default_name):
filename = dname
try:
workbook = openpyxl.load_workbook(filename)
except:
print("No file")
return
sheet = workbook.active
columns = sheet.max_column
rows= str(sheet.max_row)
max_column_letter = chr(ord("A")+ number_of_columns -1 )
raw= sheet['A1': max_column_letter+number_of_rows]
data= []
for row in raw:
sublist = []
for cell in raw:
sublist.append(cell.value)
data.append(sublist)
return(data) #creates a list of list
The error i get is "builtins.NameError: name 'data' is not defined"
Im having trouble, taking 'data' from open_file(dname) and having it being a parameter for create_animal_dict, I was wondering how to to bring a variable from one helper function to another.
Thanks for any help or tips!
You are not receiving the output from your open_excel function, which then I assume needs to be passed to the create_animal_dict function, e.g.
def file_open(dname, dict, animal):
data = open_excel(dname)
create_animal_dict(mainlist, dict, data)
I assume the error is coming from you calling data from inside create_animal_dict, which this would solve.
But you should also take the output from create_animal_dict and pass it back to main function if you are structuring your program this way.
I have a code as follows:
class SifFile():
setting = {}
interesting_param = ['Temp', 'Pressure']
def __init__(self, get_param):
self.File_Type = "Andor Technology Multi-Channel File"
for k, v in get_param.items():
if SifFile.interesting_param in k:
SifFile.setting[k] = v
return SifFile.setting
get_parameter = {'Temp':75, 'Pressure':50, 'Helium':90, 'Exp':96}
sif = SifFile(get_parameter)
There is a big dict named get_parameter that has a few parameters and their values.
There is also a list named interesting_param that contains 2 elements.
What I want to do is to check which parameters from interesting_param list are present in the get_parameter dictionary and I want to save those parameters in an empty dict named setting
I tried running the above code, but it gives me the following error:
Traceback (most recent call last):
File "", line 16, in
sif = SifFile(get_parameter)
File "", line 8, in init
if SifFile.interesting_param in k:
TypeError: 'in ' requires string as left operand, not list
Expected output:
setting = {'Temp':75, 'Pressure':50}
Here is the code that will give you the expected answer:
class SifFile():
setting = {}
interesting_param = ['Temp', 'Pressure']
def __init__(self):
self.File_Type = "Andor Technology Multi-Channel File"
return
def func(self, get_param):
for k, v in get_param.items():
if k in SifFile.interesting_param:
SifFile.setting[k] = v
return SifFile.setting
get_parameter = {'Temp':75, 'Pressure':50, 'Helium':90, 'Exp':96}
sif = SifFile()
x=sif.func(get_parameter)
print(x)
I have created anothter funcion called "func" because "init()" cannot return a dictionary. It should only return "None".
Besides that, the condition statement within the for loop is changed.
The error is telling you what's wrong: you are trying to check if a key exists in a dict but the key that you're checking for isn't a string. Let's look at the line in question:
if SifFile.interesting_param in k:
The error thinks that SifFile.interesting_param is a list, so let's have a look at where you define that:
interesting_param = ['Temp', 'Pressure']
Oh yeah, that is a list. Since a list can't be a dict key it throws an error.
You need to loop through your items in interesting_param one by one to check whether they're in the dict. I've implemented that here, along with a range of other issues in your code, mainly surrounding how you'd implemented the class:
class SifFile():
"""
Class for holding and processing sif files.
"""
def __init__(self, params):
"""
Define the variables you want to use in your class
"""
self.file_type = "Andor Technology Multi-Channel File"
self.interesting_params = ['Temp', 'Pressure']
self.given_params = params
self.setting = {}
def get_settings(self):
"""
Return list of settings of interest
"""
# Look at every parameter of interest in turn
for param in self.interesting_params:
# Check to see if it is in the dict of given parameters
if param in self.given_params:
# If it is then add it to the setting dict
self.setting[param] = self.given_params[param]
# Return the setting dict once the loop is done
return self.setting
parameters = {'Temp':75, 'Pressure':50, 'Helium':90, 'Exp':96}
sif = SifFile(parameters)
print(sif.get_settings())
Note that your variables are now all instance variables rather than class variables (they start with self) because you're changing them, so they are unlikely to be the same for every class.