String Operations in Python

This tutorial gives an introduction to string operations in Python: Starting with joining strings, determining the length and using the index operator to access individual characters, we also show how to iterate over strings, searching and comparing strings and briefly explain the standard methods for strings in Python.

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Python String cheat-sheet Strings Index Operator
Table of contents

Length of a string

One can determine the length of a string using the function len() :

jberries = 'jberries'
len(jberries) # => 8

The Python interpreter provides a wide range of built-in functions and types that are accessible for use in any given script. The <a href="https://docs.python.org/3/library/functions.html#len">len</a> function belongs also to the build-in functions in Python.

Concatenating strings

To concatenate strings, you can use the plus "+" operator as often seen in other programming languages:

foo = "foo"
bar = "bar"
print(foo + bar) # => foobar

However, Python does not automatically convert to string if one of the variables is not a string, and in this case, it raises an error. In such cases, we can simply use the "str() " function:

foo = "foo"
bar = 5
print(foo + bar) # => TypeError: can only concatenate str (not "int") to str
print(foo + str(bar)) # => foo5

Strings and the index operator

With the "index operator," one can access the individual characters of a string in Python. It is very easy, for example, to extract the first or last x characters of a string or access a specific character. The index operator can handle both positive and negative indices:

12345678
jberries
-8-7-6-5-4-3-2-1

Here are some examples:

All characters from the 1st character on

print(jberries[1:]) # => berries

Characters between index 2 and 5

print(jberries[2:5]) # => err

The last 3 characters

print(jberries[-3:]) # => ies

The first two characters

print(jberries[:-6]) # => jb
# or
print(jberries[0:2]) # => jb

The penultimate character

print(jberries[-2]) # => e

Reverse the order of characters (invert string)

jberries = 'jberries'
jberries_inv = jberries[::-1]
print(jberries_inv) # => seirrebj

String/Byte conversion and Encoding

Converting a string with utf-8 encoding into a byte array:

test = bytes("😀JBerries", encoding = \'utf-8\'),

Afterwards, we can transform the byte array back into a string:

str(test, encoding = "ascii", errors ="ignore") # => JBerries

Here we have selected the ASCII encoding, which does not include the smiley character, and with errors ="ignore" , we suppress the error that would otherwise be thrown.

Iterating over strings

The simplest way is with a for loop:

for c in "jberries":
  print (c)

If we only want to iterate over a part of the string, we can use range in the for loop for this purpose:

jb = "jberries"
for i in range(2, 4):
    print(jb[i])
# => e
# => r

Checking if another string is contained in a string

This is very simple again in Python:

if "jb" in "jberries":
    print("jb is in jberries")
# => jb is in jberries

Common string methods

(s = " Hello World " print(s.strip()) # Output: Hello World)