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Decorating on function defined within loop [duplicate]

This question already has answers here:
Creating functions (or lambdas) in a loop (or comprehension)
(6 answers)
Closed 1 year ago.
I believe this is a similar case, however, I'm not sure how to apply the solutions to my case.
I am creating a function within a loop that is supplied by an argument. The function is called later, but it is stored for later and is supplied with the argument.
for type_str in ["type_1", "type_2", "type_3"]:
#decorator_exec.register(...)
def to_exec(num: int):
print(type_str, num)
# later...
# this is an example
i = 0
for func in decorator_exec.funcs:
func(i)
i++
Unfortunately, this is what would be produced:
type_3 0
type_3 1
type_3 2
I would like the output to ensure that the type_str variable (and any other variables that are included in to_exec() body), be what it should be when it is defined.
type_1 0
type_2 1
type_3 2
The to_exec() that is within the loop isn't used later within the loop, or outside the loop. It is solely stored by the decorator code and is called from its stored functions later.
If it isn't an XY problem, a possible solution would be to use a function factory (I'm not sure how that would work...)

You are not storing the functions for later, you are assigning three functions to the same name, so the last one is what sticks: the previous two get overwritten by the next one.
You can achieve what you're looking for with something like this:
# This is a dictionary created with a dict comprehension.
functions = {
# A decorator is just a function that takes a function and
# returns a function, so you can call it like a normal
# function. The first argument is your own function,
# and the result will be the decorated function.
type_str: decorator_exec.register(
# This is an anonymous function. You don't need to give
# a name to the function in this case because it will
# be called with the dict key it's stored in anyway.
lambda num: print(type_str, num),
..., # Any arguments the decorator needs
)
for type_str in ["type_1", "type_2", "type_3"]
}
This will create a dictionary with one entry per string in your list, such that functions["type_1"] will have the function defined with "type_1" and so on, which you can call, for example, like this: functions["type_2"](420).
You could achieve the same by adding each entry to an empty dict using a for loop, but comprehensions are usually more idiomatic. Because of the decorator, in this case it's probably more readable to do it the wordy way (and it allows you to use type annotations too):
functions = {}
for type_str in ["type_1", "type_2", "type_3"]:
#decorator_exec.register(...)
def the_func(num: int):
print(type_str, num)
functions[type_str] = the_func
The key takeaway is that you cannot use the same name more than once and expect different results, so you have to store your functions in a data structure. If you don't care about the name of the functions at all, you can use a list instead of a dictionary, and simply retrieve/call each function with its index.

You need to keep the reference to the correct string in memory. you can do that by accessing the items with an index variable.
The 2 first lines are relevant for this.
The rest is just to provide a working example,
def generate_funcs(xs, i=0):
return [lambda x: print(xs[i], x)] + generate_funcs(xs, i+1) if i<len(xs) else []
f = generate_funcs(["type_1", "type_2", "type_3"])
for (func, i) in zip(f, range(len(f))):
func(i)

Python: Using variables and content established in the main module without passing them as an explicit argument in the function definition

I am relatively new to python (and programming). I would like to understand what items, content, variables need to be passed as an explicit argument in the function definition and what can be used without being passed as an argument.
It seems that if a variable or item is introduced/defined in the module where the function is later located that it does not need to be passed as an argument.
Perhaps the below example from Codecademy will help to illustrate my question. Here we access the values from the created dictionaries stock and prices without passing either as an argument.
shopping_list = ["banana", "orange", "apple"]
stock = {
"banana": 6,
"apple": 0,
"orange": 32,
"pear": 15
}
prices = {
"banana": 4,
"apple": 2,
"orange": 1.5,
"pear": 3
}
def compute_bill(food):
total = 0
for item in food:
if stock[item] > 0:
total += prices[item]
stock[item] -= 1
return total

You can define a variable first, and then pass it to the function or loop just to initialize the variable ahead of time:
For instance:
i = 0
for i in some_list:
do something
i += 1
This will allow you to create i to 0 first and then loop through a list of an undetermined length and increment i to count over each item. If you were to try to run this function again however, it would do nothing as i has been increased and stays that way. You would need to reset i back to 0 or close out the interpreter and re-run the program.
Functions can do many different things. Say you want to say hello to someone:
def hello(name):
name = name
print(Hello, {}.format(name))
hello("Peter")
Output would be:
Hello, Peter
With this you can pass a variable without defining it, and it will store it inside of that function. If you try and call the "name" variable outside of the function though, you will get an error as its scope is only for that function. I hope this makes since and I highly recommend reading up more on Python Scope on their website here https://docs.python.org/3/tutorial/index.html This will tell you everything you need to know about functions in python.
Also as an aside, the reason the dictionaries are not passed as an argument in your example, is because we are using a For loop to iterate over the values. Look into For loops at the link I provided. Basically it is counting over each loop through and grabbing the prices of each item, and dynamically passing the location to each item via the "item" variable. once it reaches the end of the dictionary, it is giving you a total price, along with deducting inventory off the stock dictionary. So they are being used, but for a For loop in python there is no need to pass them as parameters. Now if you were to compare the two together, and your function was written in a way to take two dictionaries or strings as values to compare, then you would either need to define them in the function parameter itself, or create them ahead of time and pass the variable as a parameter.
Clarification:
So say you want to compare whats different in two dictionaries as a function. You can pass the dictionaries like so as parameters:
d1 = {'a': 912,'b':256,'c':350}
d2 = {'b':256,'x':290,'a':912}
def compare(a, b):
diff1 = set(a.items()) - set(b.items())
diff2 = set(b.items()) - set(a.items())
print(diff1)
print(diff2)
compare(d1,d2)
Output would be:
{('c', 350)}
{('x', 290)}
As you can see, we defined the dictionaries first, then passed them as arguments to the function to see what was different between the two.
You can even define the dictionaries on the fly:
compare({'a': 912, 'b': 256, 'c': 350}, {'b': 256, 'x': 290, 'a': 912})
Results remain the same.
You can also explicitly define they are used in the function directly but will limit the ability to use this function on any other dictionaries you wanted to compare.
d1 = {'a': 912,'b':256,'c':350}
d2 = {'b':256,'x':290,'a':912}
def compare():
diff1 = set(d1.items()) - set(d2.items())
diff2 = set(d2.items()) - set(d1.items())
print(diff1)
print(diff2)
compare()
Output remains the same as above. As you can see, we pass no arguments, and simply just compare the results and call that through:
compare()
It makes more sense though to pass arguments in this case, so you can compare multiple dictionaries anywhere in your program. Hope that clears that up some.

You can use python classes to initialize variables in the constructor and use them in the methods if you have many methods . So you can avoid passing same arguments to all functions
https://docs.python.org/3/tutorial/classes.html

In order to know how those list and dictionary is accessible in function defined later, you should know how python looks and resolves variables.
Look for local variable with same name if found use it
If no local variable is found then look for global variable if found then use it.
If global variable is not found then look for environment variable.(in sys.path) if found use that.
If variable doesn't exist then raise an error.
Looking for a variable is also like looking for a function . It is because of that you can also import python variables like importing a function. I hope you know this.

How to simplify several functions with the same purpose

Let's say I have several functions that basically do the same thing but on a set of different variables. I think about something like that:
def changex():
if x:
# do procedure1 with x as variable
else:
# do procedure2 with x as variable
def changey():
if y:
# do procedure1 with y as variable
else:
# do procedure2 with y as variable
def changez():
...
How can I simplify that set of functions, such that I only have to write the function once but it does the job for all variables? I already looked into decorators which I think can do the job, but I can't make out how to make it work for my purpose.

Functions can accept variables as parameters.
Something like this:
def change(p):
if p:
# do procedure1 with p as variable
else:
# do procedure2 with p as variable
Then changex() becomes change(x); changey() becomes change(y) etc.

Decorators are way too complex for what you are trying to do. Functions can take arguments, so you can pass in the variable you want to do stuff with:
def change(var):
if var:
procedure1(var)
else:
procedure2(var)
Notice that I used if/else instead of checking both conditions with an if. I also recommend not testing explicitly against True/False. If you must do so, however, it is considered better practice to use is instead of == since True and False are singleton objects in Python: if x is True is better than if x == True.

How to get the name of lists for comparison purposes

This may sound a bit funny, but this is what am trying to do:
I have two lists: myList1 and myList2. I am passing these lists to a function that will perform a specific task depending on which list it receives (i.e., based on the name of the list, not content).
def listProcessor(data):
if data == 'myList1':
perform task1
else: #meaning data is myList2
perform task 2
Is there a way in Python 3 to inquire of the name of a list (or a tuple, dictionary, etc.) and do a comparison like this? Obviously, the way I am doing it here isn't working since it's comparing the content of the list 'data' to the single string 'myList1', which isn't working! :-).

There are a few ways to do this:
You can create separate functions if what needs to be done for each list really is completely separate.
You can update your function to either:
Take two lists as an argument:
def list_processor(list1=None, list2=None):
if list1:
# do stuff for list1
if list2:
# do stuff for list2
You can add an extra flag, identifying what kind of action to be performed, and set a default as well:
def list_processor(some_list=None, type_of_list=1):
if type_of_list == 1:
# do stuff with some_list as if it was list1
if type_of_list == 2:
# do stuff with some_list as if it was list2
You do not want to do what you initially proposed, for various reasons. One key reason is that in Python, what you may call variables in other languages are not "boxes to put stuff in" (as most textbooks refer to them).
In Python variables are actually just names that point to an object. The key thing is that multiple names can point to the same object; which will easily confuse your function if you rely on the lists "name".
Here is an example:
>>> a = [1,2,3]
>>> b = a
>>> b.append('hello')
>>> b is a
True
>>> b == a
True
>>> b
[1, 2, 3, 'hello']
>>> a
[1, 2, 3, 'hello']
In this example, both a and b are pointing to the same list object. What you do with a affects b.

So let's start with this: you really shouldn't do this. Data is just data in Python -- the identifier (e.g. the name you're using to talk about it) means nothing to the program logic itself. It's only meaningful to the programmer.
That said, there's ways to do what you're trying to do, and they're all the wrong thing to do. But they're possible, so let's talk about them.
globals() will give you a dictionary with keys of identifiers and values of, um, values, for all objects currently in the global scope. This means that you can do:
def list_processor(data):
g = globals()
data_name = next((k for k,v in g.items() if v is data))
if data_name == 'myList1':
... # do whatever you want here
Note, however, that you're looking through EVERYTHING in the global scope. First off, that's dumb since it's slow, and secondly, it's dumb because it's buggy. What if myList1 isn't being passed from the global scope? What if it's a local variable inside a function that never hits the global scope? Now your tricky hack fails.
The correct way to do this is to perform some sort of introspection on the argument being passed in as "data". For instance if myList1 always has 8 elements and myList2 always has 10:
def f_if_myList1(lst):
"""Do whatever we do if we pass myList1"""
...
def f_if_myList2(lst):
"""Do whatever we do if we pass myList2"""
...
def list_processor(data):
if len(data) == 8: # myList1!
f_if_myList1(data)
elif len(data) == 10:
f_if_myList2(data)
else:
# not sure. raise ValueError()?

Get array name in function it is passed to [duplicate]

I already read How to get a function name as a string?.
How can I do the same for a variable? As opposed to functions, Python variables do not have the __name__ attribute.
In other words, if I have a variable such as:
foo = dict()
foo['bar'] = 2
I am looking for a function/attribute, e.g. retrieve_name() in order to create a DataFrame in Pandas from this list, where the column names are given by the names of the actual dictionaries:
# List of dictionaries for my DataFrame
list_of_dicts = [n_jobs, users, queues, priorities]
columns = [retrieve_name(d) for d in list_of_dicts]

With Python 3.8 one can simply use f-string debugging feature:
>>> foo = dict()
>>> f'{foo=}'.split('=')[0]
'foo'
One drawback of this method is that in order to get 'foo' printed you have to add f'{foo=}' yourself. In other words, you already have to know the name of the variable. In other words, the above code snippet is exactly the same as just
>>> 'foo'

Even if variable values don't point back to the name, you have access to the list of every assigned variable and its value, so I'm astounded that only one person suggested looping through there to look for your var name.
Someone mentioned on that answer that you might have to walk the stack and check everyone's locals and globals to find foo, but if foo is assigned in the scope where you're calling this retrieve_name function, you can use inspect's current frame to get you all of those local variables.
My explanation might be a little bit too wordy (maybe I should've used a "foo" less words), but here's how it would look in code (Note that if there is more than one variable assigned to the same value, you will get both of those variable names):
import inspect
x, y, z = 1, 2, 3
def retrieve_name(var):
callers_local_vars = inspect.currentframe().f_back.f_locals.items()
return [var_name for var_name, var_val in callers_local_vars if var_val is var]
print(retrieve_name(y))
If you're calling this function from another function, something like:
def foo(bar):
return retrieve_name(bar)
foo(baz)
And you want the baz instead of bar, you'll just need to go back a scope further. This can be done by adding an extra .f_back in the caller_local_vars initialization.
See an example here: ideone

The only objects in Python that have canonical names are modules, functions, and classes, and of course there is no guarantee that this canonical name has any meaning in any namespace after the function or class has been defined or the module imported. These names can also be modified after the objects are created so they may not always be particularly trustworthy.
What you want to do is not possible without recursively walking the tree of named objects; a name is a one-way reference to an object. A common or garden-variety Python object contains no references to its names. Imagine if every integer, every dict, every list, every Boolean needed to maintain a list of strings that represented names that referred to it! It would be an implementation nightmare, with little benefit to the programmer.

TL;DR
Use the Wrapper helper from python-varname:
from varname.helpers import Wrapper
foo = Wrapper(dict())
# foo.name == 'foo'
# foo.value == {}
foo.value['bar'] = 2
For list comprehension part, you can do:
n_jobs = Wrapper(<original_value>)
users = Wrapper(<original_value>)
queues = Wrapper(<original_value>)
priorities = Wrapper(<original_value>)
list_of_dicts = [n_jobs, users, queues, priorities]
columns = [d.name for d in list_of_dicts]
# ['n_jobs', 'users', 'queues', 'priorities']
# REMEMBER that you have to access the <original_value> by d.value
I am the author of the python-varname package. Please let me know if you have any questions or you can submit issues on Github.
The long answer
Is it even possible?
Yes and No.
We are retrieving the variable names at runtime, so we need a function to be called to enable us to access the previous frames to retrieve the variable names. That's why we need a Wrapper there. In that function, at runtime, we are parsing the source code/AST nodes in the previous frames to get the exact variable name.
However, the source code/AST nodes in the previous frames are not always available, or they could be modified by other environments (e.g: pytest's assert statement). One simple example is that the codes run via exec(). Even though we are still able to retrieve some information from the bytecode, it needs too much effort and it is also error-prone.
How to do it?
First of all, we need to identify which frame the variable is given. It's not always simply the direct previous frame. For example, we may have another wrapper for the function:
from varname import varname
def func():
return varname()
def wrapped():
return func()
x = wrapped()
In the above example, we have to skip the frame inside wrapped to get to the right frame x = wrapped() so that we are able to locate x. The arguments frame and ignore of varname allow us to skip some of these intermediate frames. See more details in the README file and the API docs of the package.
Then we need to parse the AST node to locate where the variable is assigned value (function call) to. It's not always just a simple assignment. Sometimes there could be complex AST nodes, for example, x = [wrapped()]. We need to identify the correct assignment by traversing the AST tree.
How reliable is it?
Once we identify the assignment node, it is reliable.
varname is all depending on executing package to look for the node. The node executing detects is ensured to be the correct one (see also this).
It partially works with environments where other AST magics apply, including pytest, ipython, macropy, birdseye, reticulate with R, etc. Neither executing nor varname is 100% working with those environments.
Do we need a package to do it?
Well, yes and no, again.
If your scenario is simple, the code provided by #juan Isaza or #scohe001 probably is enough for you to work with the case where a variable is defined at the direct previous frame and the AST node is a simple assignment. You just need to go one frame back and retrieve the information there.
However, if the scenario becomes complicated, or we need to adopt different application scenarios, you probably need a package like python-varname, to handle them. These scenarios may include to:
present more friendly messages when the source code is not available or AST nodes are not accessible
skip intermediate frames (allows the function to be wrapped or called in other intermediate frames)
automatically ignores calls from built-in functions or libraries. For example: x = str(func())
retrieve multiple variable names on the left-hand side of the assignment
etc.
How about the f-string?
Like the answer provided by #Aivar Paalberg. It's definitely fast and reliable. However, it's not at runtime, meaning that you have to know it's foo before you print the name out. But with varname, you don't have to know that variable is coming:
from varname import varname
def func():
return varname()
# In external uses
x = func() # 'x'
y = func() # 'y'
Finally
python-varname is not only able to detect the variable name from an assignment, but also:
Retrieve variable names directly, using nameof
Detect next immediate attribute name, using will
Fetch argument names/sources passed to a function using argname
Read more from its documentation.
However, the final word I want to say is that, try to avoid using it whenever you can.
Because you can't make sure that the client code will run in an environment where the source node is available or AST node is accessible. And of course, it costs resources to parse the source code, identify the environment, retrieve the AST nodes and evaluate them when needed.

On python3, this function will get the outer most name in the stack:
import inspect
def retrieve_name(var):
"""
Gets the name of var. Does it from the out most frame inner-wards.
:param var: variable to get name from.
:return: string
"""
for fi in reversed(inspect.stack()):
names = [var_name for var_name, var_val in fi.frame.f_locals.items() if var_val is var]
if len(names) > 0:
return names[0]
It is useful anywhere on the code. Traverses the reversed stack looking for the first match.

I don't believe this is possible. Consider the following example:
>>> a = []
>>> b = a
>>> id(a)
140031712435664
>>> id(b)
140031712435664
The a and b point to the same object, but the object can't know what variables point to it.

def name(**variables):
return [x for x in variables]
It's used like this:
name(variable=variable)

>> my_var = 5
>> my_var_name = [ k for k,v in locals().items() if v == my_var][0]
>> my_var_name
'my_var'
In case you get an error if myvar points to another variable, try this (suggested by #mherzog)-
>> my_var = 5
>> my_var_name = [ k for k,v in locals().items() if v is my_var][0]
>> my_var_name
'my_var'
locals() - Return a dictionary containing the current scope's local variables.
by iterating through this dictionary we can check the key which has a value equal to the defined variable, just extracting the key will give us the text of variable in string format.
from (after a bit changes)
https://www.tutorialspoint.com/How-to-get-a-variable-name-as-a-string-in-Python

I wrote the package sorcery to do this kind of magic robustly. You can write:
from sorcery import dict_of
columns = dict_of(n_jobs, users, queues, priorities)
and pass that to the dataframe constructor. It's equivalent to:
columns = dict(n_jobs=n_jobs, users=users, queues=queues, priorities=priorities)

Here's one approach. I wouldn't recommend this for anything important, because it'll be quite brittle. But it can be done.
Create a function that uses the inspect module to find the source code that called it. Then you can parse the source code to identify the variable names that you want to retrieve. For example, here's a function called autodict that takes a list of variables and returns a dictionary mapping variable names to their values. E.g.:
x = 'foo'
y = 'bar'
d = autodict(x, y)
print d
Would give:
{'x': 'foo', 'y': 'bar'}
Inspecting the source code itself is better than searching through the locals() or globals() because the latter approach doesn't tell you which of the variables are the ones you want.
At any rate, here's the code:
def autodict(*args):
get_rid_of = ['autodict(', ',', ')', '\n']
calling_code = inspect.getouterframes(inspect.currentframe())[1][4][0]
calling_code = calling_code[calling_code.index('autodict'):]
for garbage in get_rid_of:
calling_code = calling_code.replace(garbage, '')
var_names, var_values = calling_code.split(), args
dyn_dict = {var_name: var_value for var_name, var_value in
zip(var_names, var_values)}
return dyn_dict
The action happens in the line with inspect.getouterframes, which returns the string within the code that called autodict.
The obvious downside to this sort of magic is that it makes assumptions about how the source code is structured. And of course, it won't work at all if it's run inside the interpreter.

This function will print variable name with its value:
import inspect
def print_this(var):
callers_local_vars = inspect.currentframe().f_back.f_locals.items()
print(str([k for k, v in callers_local_vars if v is var][0])+': '+str(var))
***Input & Function call:***
my_var = 10
print_this(my_var)
***Output**:*
my_var: 10

>>> locals()['foo']
{}
>>> globals()['foo']
{}
If you wanted to write your own function, it could be done such that you could check for a variable defined in locals then check globals. If nothing is found you could compare on id() to see if the variable points to the same location in memory.
If your variable is in a class, you could use className.dict.keys() or vars(self) to see if your variable has been defined.

I have a method, and while not the most efficient...it works! (and it doesn't involve any fancy modules).
Basically it compares your Variable's ID to globals() Variables' IDs, then returns the match's name.
def getVariableName(variable, globalVariables=globals().copy()):
""" Get Variable Name as String by comparing its ID to globals() Variables' IDs
args:
variable(var): Variable to find name for (Obviously this variable has to exist)
kwargs:
globalVariables(dict): Copy of the globals() dict (Adding to Kwargs allows this function to work properly when imported from another .py)
"""
for globalVariable in globalVariables:
if id(variable) == id(globalVariables[globalVariable]): # If our Variable's ID matches this Global Variable's ID...
return globalVariable # Return its name from the Globals() dict

In Python, the def and class keywords will bind a specific name to the object they define (function or class). Similarly, modules are given a name by virtue of being called something specific in the filesystem. In all three cases, there's an obvious way to assign a "canonical" name to the object in question.
However, for other kinds of objects, such a canonical name may simply not exist. For example, consider the elements of a list. The elements in the list are not individually named, and it is entirely possible that the only way to refer to them in a program is by using list indices on the containing list. If such a list of objects was passed into your function, you could not possibly assign meaningful identifiers to the values.
Python doesn't save the name on the left hand side of an assignment into the assigned object because:
It would require figuring out which name was "canonical" among multiple conflicting objects,
It would make no sense for objects which are never assigned to an explicit variable name,
It would be extremely inefficient,
Literally no other language in existence does that.
So, for example, functions defined using lambda will always have the "name" <lambda>, rather than a specific function name.
The best approach would be simply to ask the caller to pass in an (optional) list of names. If typing the '...','...' is too cumbersome, you could accept e.g. a single string containing a comma-separated list of names (like namedtuple does).

I think it's so difficult to do this in Python because of the simple fact that you never will not know the name of the variable you're using. So, in his example, you could do:
Instead of:
list_of_dicts = [n_jobs, users, queues, priorities]
dict_of_dicts = {"n_jobs" : n_jobs, "users" : users, "queues" : queues, "priorities" : priorities}

Many of the answers return just one variable name. But that won't work well if more than one variable have the same value. Here's a variation of Amr Sharaki's answer which returns multiple results if more variables have the same value.
def getVariableNames(variable):
results = []
globalVariables=globals().copy()
for globalVariable in globalVariables:
if id(variable) == id(globalVariables[globalVariable]):
results.append(globalVariable)
return results
a = 1
b = 1
getVariableNames(a)
# ['a', 'b']

just another way to do this based on the content of input variable:
(it returns the name of the first variable that matches to the input variable, otherwise None. One can modify it to get all variable names which are having the same content as input variable)
def retrieve_name(x, Vars=vars()):
for k in Vars:
if isinstance(x, type(Vars[k])):
if x is Vars[k]:
return k
return None

If the goal is to help you keep track of your variables, you can write a simple function that labels the variable and returns its value and type. For example, suppose i_f=3.01 and you round it to an integer called i_n to use in a code, and then need a string i_s that will go into a report.
def whatis(string, x):
print(string+' value=',repr(x),type(x))
return string+' value='+repr(x)+repr(type(x))
i_f=3.01
i_n=int(i_f)
i_s=str(i_n)
i_l=[i_f, i_n, i_s]
i_u=(i_f, i_n, i_s)
## make report that identifies all types
report='\n'+20*'#'+'\nThis is the report:\n'
report+= whatis('i_f ',i_f)+'\n'
report+=whatis('i_n ',i_n)+'\n'
report+=whatis('i_s ',i_s)+'\n'
report+=whatis('i_l ',i_l)+'\n'
report+=whatis('i_u ',i_u)+'\n'
print(report)
This prints to the window at each call for debugging purposes and also yields a string for the written report. The only downside is that you have to type the variable twice each time you call the function.
I am a Python newbie and found this very useful way to log my efforts as I program and try to cope with all the objects in Python. One flaw is that whatis() fails if it calls a function described outside the procedure where it is used. For example, int(i_f) was a valid function call only because the int function is known to Python. You could call whatis() using int(i_f**2), but if for some strange reason you choose to define a function called int_squared it must be declared inside the procedure where whatis() is used.

Maybe this could be useful:
def Retriever(bar):
return (list(globals().keys()))[list(map(lambda x: id(x), list(globals().values()))).index(id(bar))]
The function goes through the list of IDs of values from the global scope (the namespace could be edited), finds the index of the wanted/required var or function based on its ID, and then returns the name from the list of global names based on the acquired index.

Whenever I have to do it, mostly while communicating json schema and constants with the frontend I define a class as follows
class Param:
def __init__(self, name, value):
self.name = name
self.value = value
Then define the variable with name and value.
frame_folder_count = Param({'name':'frame_folder_count', 'value':10})
Now you can access the name and value using the object.
>>> frame_folder_count.name
'frame_folder_count'

>>> def varname(v, scope=None):
d = globals() if not scope else vars(scope); return [k for k in d if d[k] == v]
...
>>> d1 = {'a': 'ape'}; d2 = {'b': 'bear'}; d3 = {'c': 'cat'}
>>> ld = [d1, d2, d3]
>>> [varname(d) for d in ld]
[['d1'], ['d2'], ['d3']]
>>> d5 = d3
>>> [varname(d) for d in ld]
[['d1'], ['d2'], ['d3', 'd5']]
>>> def varname(v, scope=None):
d = globals() if not scope else vars(scope); return [k for k in d if d[k] is v]
...
>>> [varname(d) for d in ld]
[['d1'], ['d2'], ['d3', 'd5']]
As you see and is noted here, there can be multiple variables with the same value or even address, so using a wrapper to keep the names with the data is best.

Following method will not return the name of variable but using this method you can create data frame easily if variable is available in global scope.
class CustomDict(dict):
def __add__(self, other):
return CustomDict({**self, **other})
class GlobalBase(type):
def __getattr__(cls, key):
return CustomDict({key: globals()[key]})
def __getitem__(cls, keys):
return CustomDict({key: globals()[key] for key in keys})
class G(metaclass=GlobalBase):
pass
x, y, z = 0, 1, 2
print('method 1:', G['x', 'y', 'z']) # Outcome: method 1: {'x': 0, 'y': 1, 'z': 2}
print('method 2:', G.x + G.y + G.z) # Outcome: method 2: {'x': 0, 'y': 1, 'z': 2}
A = [0, 1]
B = [1, 2]
pd.DataFrame(G.A + G.B) # It will return a data frame with A and B columns

Some of the previous cases would fail if there are two variables with the same value. So it is convenient to alert it:
Defining function:
# Variable to string of variable name
def var_name(variable,i=0):
results = []
for name in globals():
if eval(name) == variable:
results.append(name)
if len(results) > 1:
print('Warning:' )
print(' var_name() has found',len(results), 'possible outcomes.')
print(' Please choose the suitable parameter "i". Where "i" is the index')
print(' that matches your choice from the list below.')
print(' ',results) ; print('')
return results[i]
Use:
var_1 = 10
var_name(var_1) # Output will be "var_1"
If you have 2 variables with the same value like var_1 = 8 and var_2 = 8, then a warning will appear.
var_1 = 8
var_2 = 8
var_name(var_2) # Output will be "var_1" too but Warning will appear

You can get your variable as kwargs and return it as string:
var=2
def getVarName(**kwargs):
return list(kwargs.keys())[0]
print (getVarName(var = var))
Note: variable name must be equal to itself.

I try to get name from inspect locals, but it cann't process var likes a[1], b.val.
After it, I got a new idea --- get var name from the code, and I try it succ!
code like below:
#direct get from called function code
def retrieve_name_ex(var):
stacks = inspect.stack()
try:
func = stacks[0].function
code = stacks[1].code_context[0]
s = code.index(func)
s = code.index("(", s + len(func)) + 1
e = code.index(")", s)
return code[s:e].strip()
except:
return ""

You can try the following to retrieve the name of a function you defined (does not work for built-in functions though):
import re
def retrieve_name(func):
return re.match("<function\s+(\w+)\s+at.*", str(func)).group(1)
def foo(x):
return x**2
print(retrieve_name(foo))
# foo

When finding the name of a variable from its value,
you may have several variables equal to the same value,
for example var1 = 'hello' and var2 = 'hello'.
My solution:
def find_var_name(val):
dict_list = []
global_dict = dict(globals())
for k, v in global_dict.items():
dict_list.append([k, v])
return [item[0] for item in dict_list if item[1] == val]
var1 = 'hello'
var2 = 'hello'
find_var_name('hello')
Outputs
['var1', 'var2']

Compressed version of iDilip's answer:
import inspect
def varname(x):
return [k for k,v in inspect.currentframe().f_back.f_locals.items() if v is x][0]
hi = 123
print(varname(hi))

It's totally possible to get the name of an instance variable, so long as it is the property of a class.
I got this from Effective Python by Brett Slatkin. Hope it helps someone:
The class must implement the get, set, and set_name dunder methods, which are part of the "Descriptor Protocol"
This worked when I ran it:
class FieldThatKnowsItsName():
def __init__(self):
self.name = None
self._value= None
self.owner = None
def __set_name__(self, owner, name):
self.name = name
self.owner = owner
self.owner.fields[self.name] = self
def __get__(self, instance, instance_type):
return self
def __set__(self, instance, value):
self = value
class SuperTable:
fields = {}
field_1=FieldThatKnowsItsName()
field_2=FieldThatKnowsItsName()
table = SuperTable()
print(table.field_1.name)
print(table.field_2.name)
You can then add methods and or extend your datatype as you like.
As a bonus, the set_name(self, owner, name) dunder also passes the parent instance, so the Field class instance can register itself with the parent.
I got this from Effective Python by Brett Slatkin. It took a while to figure out how to implement.

How can I do the same for a variable? As opposed to functions, Python variables do not have the __name__ attribute.
The problem comes up because you are confused about terminology, semantics or both.
"variables" don't belong in the same category as "functions". A "variable" is not a thing that takes up space in memory while the code is running. It is just a name that exists in your source code - so that when you're writing the code, you can explain which thing you're talking about. Python uses names in the source code to refer to (i.e., give a name to) values. (In many languages, a variable is more like a name for a specific location in memory where the value will be stored. But Python's names actually name the thing in question.)
In Python, a function is a value. (In some languages, this is not the case; although there are bytes of memory used to represent the actual executable code, it isn't a discrete chunk of memory that your program logic gets to interact with directly.) In Python, every value is an object, meaning that you can assign names to it freely, pass it as an argument, return it from a function, etc. (In many languages, this is not the case.) Objects in Python have attributes, which are the things you access using the . syntax. Functions in Python have a __name__ attribute, which is assigned when the function is created. Specifically, when a def statement is executed (in most languages, creation of a function works quite differently), the name that appears after def is used as a value for the __name__ attribute, and also, independently, as a variable name that will get the function object assigned to it.
But most objects don't have an attribute like that.
In other words, if I have a variable such as:
That's the thing: you don't "have" the variable in the sense that you're thinking of. You have the object that is named by that variable. Anything else depends on the information incidentally being stored in some other object - such as the locals() of the enclosing function. But it would be better to store the information yourself. Instead of relying on a variable name to carry information for you, explicitly build the mapping between the string name you want to use for the object, and the object itself.