For example, I get a string:

str = "please answer my question"

I want to write it to a file.

But I need to know the size of the string before writing the string to the file. What function can I use to calculate the size of the string?

If you are talking about the length of the string, you can use len():

>>> s="please answer my question"
>>> len(s)  # number of characters in s
25

If you need the size of the string in bytes, you need sys.getsizeof():

>>> import sys
>>> sys.getsizeof(s)
58

Also, don’t call your string variable str. It shadows the built-in str() function.

Python 3:

user225312’s answer is correct:

A. To count number of characters in str object, you can use len() function:

>>> print(len('please anwser my question'))
25

B. To get memory size in bytes allocated to store str object, you can use sys.getsizeof() function

>>> from sys import getsizeof
>>> print(getsizeof('please anwser my question'))
50

Python 2:

It gets complicated for Python 2.

A. The len() function in Python 2 returns count of bytes allocated to store encoded characters in a str object.

Sometimes it will be equal to character count:

>>> print(len('abc'))
3

But sometimes, it won’t:

>>> print(len('???'))  # String contains Cyrillic symbols
6

That’s because str can use variable-length encoding internally. So, to count characters in str you should know which encoding your str object is using. Then you can convert it to unicode object and get character count:

>>> print(len('???'.decode('utf8'))) #String contains Cyrillic symbols 
3

B. The sys.getsizeof() function does the same thing as in Python 3 – it returns count of bytes allocated to store the whole string object

>>> print(getsizeof('???'))
27
>>> print(getsizeof('???'.decode('utf8')))
32

>>> s="abcd"
>>> len(s)
4

You also may use str.len() to count length of element in the column

data['name of column'].str.len() 

The most Pythonic way is to use the len(). Keep in mind that the ‘\’ character in escape sequences is not counted and can be dangerous if not used correctly.

>>> len('foo')
3
>>> len('\foo')
3
>>> len('\xoo')
  File "<stdin>", line 1
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-1: truncated \xXX escape

Do you want to find the length of the string in python language ? If you want to find the length of the word, you can use the len function.

string = input("Enter the string : ")

print("The string length is : ",len(string))

OUTPUT : –

Enter the string : viral

The string length is : 5