Why can't I use the split() method in Python to split a string into a list from within a functi-CodePudding

I am unable to split a string into a list using a function in Python. However, when I do it without a function, it works. Here's my code:

def listAdder(list1):
    """ Function to split a string into a list. """
    text_line = "This is a string"
    list1 = text_line.split(' ')
    print(list1)    # printing the list to verify its status within the function.

list1 = []
listAdder(list1)
print(len(list1))    # printing the length of the list to verify its status outside the 
                     # function

The output:

['This', 'is', 'a', 'string']
0

The list is successfully created with the string elements split inside it within the function, as is evident from the output. However, the list remains empty when I try to verify its state out of the function.

What do I need to do to make the list retain its value outside the function?

CodePudding user response：

You have to assign the updated list (by your function) to another variable in your main program, like below. Inside the listAdder function only a copy of the list1 variable declared in your main program body is modified, that change will not reflect in main body unless you return a copy of it from your function.

def listAdder(list1):
    text_line = "This is a string"
    list1 = text_line.split(' ')
    print(list1)    # printing the list to verify its status within the function.
    return list1

list2 = listAdder(list1)
print(len(list2))

CodePudding user response：

This is because of the scope of variables. Updating list1 in the function does not update that object outside the scope of the function.

You can use a function without parameters and mark it with global list1, which allows it to alter list1 that you have declared in the global scope.

def listAdder():
    global list1 # This allows it to modify the variable
    """ Function to split a string into a list. """
    text_line = "This is a string"
    list1 = text_line.split(' ')

list1 = []
listAdder() # No parameter
print(len(list1)) # Prints 4

This is considered poor practice, however, as it can be harder to reason about our code.

It is better to use a function to return a value.

def listAdder():
    text_line = "This is a string"
    return text_line.split(' ')

list1 = []
list1 = listAdder()