How do I apply this string length function to a column in my dataframe?

Question

I have written a function that returns the length of a string,

def string_length():
string = input("Please enter a string: ")
"""This prompts the user to enter a string"""
return(len(string))

I have a dataset called film which has a column titled Phrase . I want to add a new column to my dataset which applies my function to the Phrase column and inputs the string length for each value in the phrase.

I tried using the following code:

film['Phrase length']=film['Phrase'].apply(string_length)

However, this returns an error:

TypeError: string_length() takes 0 positional arguments but 1 was given

What do I need to do to fix this code?

I'm sure I'm missing something very silly but I'm still quite new to python!

Answer 1

The function prompts the user for some input. This won't work if you apply it to a dataframe. You can however apply the built-in len() function:

film['Phrase length'] = film.Phrase.apply(len)

Answer 2

If I understand your question correctly then you must be looking for this:

def string_length(str):
    x = len(str)
    return x

df['Phrase length'] = df['Phrase'].apply(lambda x: string_length(x))

or,

df['Phrase length'] = df['Phrase'].map(string_length)

UPDATE:

If you want to use input() to enter the column name of your choice then use the following:

def string_length(data):
    print("Please enter column name:")
    a = input()
    data[a+'_len'] = data[a].astype(str).apply(lambda x: len(x))

followed by:

string_length(df)

Enter the column name of your choice and then try printing the dataframe.