How to Get a Substring of a String in Python

Strings in Python

A string is a sequence of characters, and each character has an index. The first has index 0.

my_string = "Hello, world!"

A substring is a part of a string. In Python you get substrings with slicing.

Slice syntax

string[start:end:step]

• start (optional) is the first index, included.
• end (optional) is the last index, excluded.
• step (optional) is the interval between characters.

Examples

Basic slicing

my_string = "Hello, World!"
substring = my_string[0:5]
print(substring)

Output: Hello

Leave out the start and the end

my_string = "Hello, World!"
print(my_string[:5])    # from the start
print(my_string[7:])    # to the end
print(my_string[:])     # a copy of the whole string

Output:

Hello
World!
Hello, World!

Negative indexes

A negative index counts from the end. -1 is the last character.

my_string = "Hello, World!"
substring = my_string[-6:-1]
print(substring)

Output: World

Use a step

my_string = "Hello, World!"
print(my_string[::2])

Output: Hlo ol!

Reverse a string with a step of -1:

print(my_string[::-1])

Output: !dlroW ,olleH

Find a specific pattern

Use find() to get the position, then slice:

text = "Contact: support@example.com for help"
start = text.find("support")
end = text.find(" for")
print(text[start:end])

Output: support@example.com

For harder patterns use regular expressions:

import re
match = re.search(r"[\w.]+@[\w.]+", text)
print(match.group())

Useful string methods

• text.split(",") splits a string into a list.
• text.partition(":") splits at the first match into 3 parts.
• text.startswith("Hel") and text.endswith("!") test the ends.
• text.index("W") is like find() but raises an error when nothing is found.
• "World" in text tests if a substring exists.

Tips

• Slicing never raises an error for indexes out of range. It just returns what exists.
• Strings are immutable: slicing makes a new string.

Quick recap

• s[start:end] cuts a substring, s[-3:] takes the last 3 characters, s[::-1] reverses.