Python String

Summary: in this tutorial, you’ll learn about Python string and its basic operations.

Introduction to Python string

A string is a series of characters. In Python, anything inside quotes is a string. And you can use either single or double quotes. For example:

message = 'This is a string in Python'
message = "This is also a string"Code language: Python (python)

If a string contains a single quote, you should place it in double-quotes like this:

message = "It's a string"Code language: Python (python)

And when a string contains double quotes, you can use the single quotes:

message = '"Beautiful is better than ugly.". Said Tim Peters'Code language: Python (python)

To escape the quotes, you use the backslash (\). For example:

message = 'It\'s also a valid string'Code language: Python (python)

The Python interpreter will treat the backslash character (\) special. If you don’t want it to do so, you can use raw strings by adding the letter r before the first quote. For example:

message = r'C:\python\bin'Code language: Python (python)

Creating multiline strings

To span a string multiple lines, you use triple-quotes “””…””” or ”’…”’. For example:

help_message = '''
Usage: mysql command
    -h hostname     
    -d database name
    -u username
    -p password 
'''

print(help_message)Code language: Python (python)

It’ll output the following if you execute the program:

Usage: mysql command
    -h hostname
    -d database name
    -u username
    -p passwordCode language: Python (python)

Using variables in Python strings with the f-strings

Sometimes, you want to use the values of variables in a string.

For example, you may want to use the value of the name variable inside the message string variable:

name = 'John'
message = 'Hi'Code language: Python (python)

To do it, you place the letter f before the opening quotation mark and put the brace around the variable name:

name = 'John'
message = f'Hi {name}'
print(message)Code language: Python (python)

Python will replace the {name} by the value of the name variable. The code will show the following on the screen:

Hi JohnCode language: Python (python)

The message is a format string, or f-string in short. Python introduced the f-string in version 3.6.

Concatenating Python strings

When you place the string literals next to each other, Python automatically concatenates them into one string. For example:

greeting = 'Good ' 'Morning!'
print(greeting)Code language: Python (python)

Output:

Good Morning!Code language: Python (python)

To concatenate two string variables, you use the operator +:

greeting = 'Good '
time = 'Afternoon'

greeting = greeting + time + '!'
print(greeting)Code language: Python (python)

Output:

Good Afternoon!Code language: Python (python)

Accessing string elements

Since a string is a sequence of characters, you can access its elements using an index. The first character in the string has an index of zero.

The following example shows how to access elements using an index:

str = "Python String"
print(str[0]) # P
print(str[1]) # yCode language: Python (python)

How it works:

• First, create a variable that holds a string "Python String".
• Then, access the first and second characters of the string by using the square brackets [] and indexes.

If you use a negative index, Python returns the character starting from the end of the string. For example:

str = "Python String"
print(str[-1])  # g
print(str[-2])  # nCode language: Python (python)

The following illustrates the indexes of the string "Python String":

+---+---+---+---+---+---+---+---+---+---+---+---+---+
| P | y | t | h | o | n |   | S | t | r | i | n | g | 
+---+---+---+---+---+---+---+---+---+---+---+---+---+
  0   1   2   3   4   5   6   7   8   9   10  11  12
-13  -12  -11  -10 -9  -8  -7  -6  -5  -4  -3  -2  -1 Code language: Python (python)

Getting the length of a string

To get the length of a string, you use the len() function. For example:

str = "Python String"
str_len = len(str)
print(str_len)Code language: Python (python)

Output:

13Code language: Python (python)

Slicing strings

Slicing allows you to get a substring from a string. For example:

str = "Python String"
print(str[0:2])Code language: Python (python)

Output:

PyCode language: Python (python)

The str[0:2] returns a substring that includes the character from the index 0 (included) to 2 (excluded).

The syntax for slicing is as follows:

string[start:end]Code language: Python (python)

The substring always includes the character at the start and excludes the string at the end.

The start and end are optional. If you omit the start, it defaults to zero. If you omit the end, it defaults to the string’s length.

Python strings are immutable

Python strings are immutable. It means that you cannot change the string. For example, you’ll get an error if you update one or more characters in a string:

str = "Python String"
str[0] = 'J'Code language: Python (python)

Error:

Traceback (most recent call last):
  File "app.py", line 2, in <module>
    str[0] = 'J'
TypeError: 'str' object does not support item assignment</module>Code language: Python (python)

When want to modify a string, you need to create a new one from the existing string. For example:

str = "Python String"
new_str = 'J' + str[1:]
print(new_str)Code language: Python (python)

Output:

Jython StringCode language: Python (python)

Summary

• In Python, a string is a series of characters. Also, Python strings are immutable.
• Use quotes, either single quotes or double quotes to create string literals.
• Use the backslash character \ to escape quotes in strings
• Use raw strings r'...' to escape the backslash character.
• Use f-strings to insert substitute variables in literal strings.
• Place literal strings next to each other to concatenate them. And use the + operator to concatenate string variables.
• Use the len() function to get the size of a string.
• Use the str[n] to access the character at the position n of the string str.
• Use slicing to extract a substring from a string.