calling a variable from a function in python error code: NoneType' object has no attribute &#03-CodePudding

Ok, maybe this is a bit of a dumb question, but my intention is to call for a variable of a function using another variable, something along this lines:

def fun():
    var1 = 100
    var2 = 'asdasd'
    var3= 24 30

x = fun()
print(x.var1)

To which I get the error mentioned in the title, is there a way to make something like this work? btw, working with python 3.9, if that helps.

CodePudding user response：

Functions on their own don't have this functionality the way you implemented it. However, there are at least 3 ways to achieve what you need (in no particular order):

1. Use scopes

Read: https://realpython.com/python-scope-legb-rule/

@quamrana gives a good TL;DR of this in their answer.

You can declare a variable in the global scope and have the function change its value.

var1 = 0

def fun():
    global var1
    var1 = 100
    var2 = 'asdasd'
    var3= 24 30

x = fun()
print(var1)

2. Create a class (lots of learning involved)

Read: https://docs.python.org/3/tutorial/classes.html

Your variables can be part of a class, and you can then use that to instantiate an object. Your function (known as a method in this case) can then modify those variables (typically called properties), and you can access those.

These concepts are the core of a paradigm called object-oriented programming, which is a concept central to Python.

class Test_class:
    def fun(self):
        self.var1 = 100
        self.var2 = 'asdasd'
        self.var3 = 24 30

test_object = Test_class()
test_object.fun()
print(test_object.var1)

3. Return the values

This is dependent on the concepts of scopes from above.

Functions can return values when control is passed back to the context calling them. With Python, you can return multiple values (using a data structure like a tuple), and choose which one to index.

def fun():
    var1 = 100
    var2 = 'asdasd'
    var3= 24 30
    return var1, var2, var3

x = fun()
print(x[0])

Any bolded term in this answer is a Googleable keyword you can use to better understand what I'm saying.

CodePudding user response：

Given your code:

def fun():
    var1 = 100
    var2 = 'asdasd'
    var3= 24 30

x = fun()

Once fun() has returned, the names: var1, var2, var3 will have disappeared and are no longer accessible.

You can have a modified version which returns three values:

def fun():
    var1 = 100
    var2 = 'asdasd'
    var3= 24 30
    return var1, var2, var3

x = fun()

Now at least the values are accessible, but still not by their previous names. Instead you could index into the returned tuple:

print(x[1])

Output:

asdasd

Also, there is another way which is to recreate the names outside the function:

def fun():
    var1 = 100
    var2 = 'asdasd'
    var3= 24 30
    return var1, var2, var3

var1, var2, var3 = fun()
print(var1, var2, var3)

Output:

100 asdasd 54

CodePudding user response：

All what you have written will work as expected if instead of a function foo was a class.

class Foo:
    var2 = 40
    def __init__(self):
        self.var1 = 100
print(Foo.var2) # 40
print(Foo().var1) # 100

In Python, a function (declared with the keyword def) doesn't have attributes, and what's more when you do something like this:

var = foo()

the variable var equals the returned value of foo(), and not foo itself.