Strings

Published Apr 29, 2021Updated Jul 27, 2022

A string is a sequence of characters contained within a pair of single quotes (') or double quotes("). Strings can store words, sentences, or whole paragraphs. They can be any length and can contain letters, numbers, symbols, and spaces.

message1 = "I am a string"
message2 = 'I am also a string'

Other data types such as integers, doubles, and booleans can also be strings if they are wrapped in quotes.

Example	String?
“2” (with double-quotes)	Yes ✅
‘3.6’ (with single-quotes)	Yes ✅
“True” (also in quotes)	Yes ✅
7 (integer)	No ❌
Hello (no quotes)	No ❌
True (boolean)	No ❌

Strings are immutable; they cannot change. Every time an operation is performed on a string, a new string is created in memory.

Accessing the Characters of a String

Strings in Python are technically a type of list — one in which each character is a separate element. This means each character in a string can be individually accessed by index, like with the elements in a list:

myString = "Hello, World!"

var_1 = myString[0]
var_2 = myString[7:]
var_3 = myString[1:4]

print("var_1: " + var_1) # Output: var_1: H
print("var_2: " + var_2) # Output: var_2: World!
print("var_3: " + var_3) # Output: var_3: ell

If an attempt is made to access an index out of bounds, it will return an IndexError.

name = "phillis"
name[8] # Throws an IndexError

Multi-line Strings

Strings can be long or short. For longer text, a multi-line string can be used. Multi-line strings begin and end with three single or double quotes:

my_string = """If it were done when 'tis done, then 'twere well
It were done quickly: if the assassination
Could trammel up the consequence, and catch
With his surcease success; that but this blow
Might be the be-all and the end-all here,
But here, upon this bank and shoal of time,
We'ld jump the life to come."""

Escape Characters

Sometimes a string may have a character that Python tries to interpret, such as '.

my_string = 'It's a lovely day!'

print(my_string)

This will raise an error, because the interpreter thinks the second ' marks the end of the string.

  File "main.py", line 1
    my_string = 'It's a lovely day!'
                    ^
SyntaxError: invalid syntax

These characters can be “escaped” by adding a backslash beforehand. The \ is called an escape character.

The backslash will not be visible if the string is printed:

my_string = 'It\'s a lovely day!'

print(my_string)
# Output: It's a lovely day!

This problem can be avoided by wrapping strings containing ' characters in double quotes:

my_string = "It's a lovely day!"

print(my_string)
# Output: It's a lovely day!

Python also has a series of non-printing characters that can modify strings. For example, \n adds a new line and \t adds a tab:

note = "I am on top!\nI am on bottom. \n\tI am indented!"

print(note)

This will output:

I am on top!
I am on bottom.
        I am indented!

Modifying Strings

Python has special operators to modify strings. For example, + can be used to concatenate strings, and * can be used to multiply a string. The keyword in can be used to see if a given character or substring exists in a string.

string_one = "Hello, "
string_two = "World! "
combo = string_one + string_two

print(combo)
# Output: Hello, World!

new_combo = combo * 2

print(new_combo)
# Output: Hello, World! Hello, World!

if "World" in new_combo:
  print("It's here!")
  # Output: It's here!

Strings can also be formatted with either of the following:

The f/F flag (placed before the opening quotation mark).
The .format() method (requires manually adding placeholders).

Comparing Strings

Python can use comparison operators to compare the contents of two strings. The operators behave as they do with numeric arguments:

Operator	Term	Description
`==`	Equal	Returns `True` if two strings are equal.
`!=`	Not equal	Returns `True` if two strings are not equal.
`<`	Less than	Returns `True` if the left string is lexically prior the right string.
`>`	Greater than	Returns `True` is the left string comes lexically after the right string.
`<=`	Less than or equal to	Returns `True` if the left string is equal to or lexically prior to the right string.
`>=`	Greater than or equal to	Returns `True` if the left string is equal to or comes lexically after the right string.

The following example demonstrates string comparison:

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Built-in String Methods

Python has a number of built-in string methods that manipulate strings. However, when these methods are called, the original string will not be changed, so any modifications will need to be saved to a new variable. A few useful built-in string methods are listed below.

Strings

.capitalize(): Takes in a string, and returns a copy of the string in capital case.
.casefold(): Returns a copy of the string with all characters in lowercase.
.center(): Returns a new string with the specified padding.
.count(): Finds the number of times the specified substring occurs within a given string.
.encode(): Encodes a given string.
.endswith(): Checks whether or not a string ends with a given value.
.find(): Takes in a substring (and optionally start/end index), return the index number of the first occurrence of the substring inside a string.
.format(): Returns a string with values inserted via placeholders.
.format_map(): Returns the values from a given dictionary.
.index(): Searches through a string variable for the occurrence of a pattern or a substring.
.isalnum(): Returns True if all the characters in a given string are alphanumeric.
.isalpha(): Returns True if all characters in a string are letters of the alphabet, otherwise it returns False.
.isascii(): Returns True if all characters in a string are ASCII characters; otherwise, it returns False.
.isdecimal(): Checks whether a string consists of only decimal characters.
.isdigit(): Checks if all the elements in the string are digits and returns a boolean flag.
.isidentifier(): Takes in a string and returns True if the string is a valid Python identifier, else returns False.
.islower(): Takes in a string and returns True if all the letters in the string are in lowercase, else returns False. Ignores spaces, newlines, numeric and special characters in the string.
.isnumeric(): Verifies that all the characters within the string variable are numeric.
.isprintable(): Returns True if all characters in the string are printable or the string is empty, otherwise False if any character in the string is nonprintable.
.isspace(): Checks if all the characters in a string are whitespace characters.
.istitle(): Checks if a given string is in title case.
.isupper(): Takes in a string and returns True if all the letters in the string are in uppercase, else returns False. Ignores spaces, newlines, numeric and special characters in the string.
.join(): Concatenates all items from an iterable into a single string.
.ljust(): Left-aligns a string with a specified fill character
.lower(): Takes a string, and returns a copy of that string in which all letters are lowercase. Numbers and symbols are not changed.
.lstrip(): Removes leading characters from a string.
.partition(): Searches a string for a given keyword and splits that string into a three part tuple.
.replace(): Replace a specific substring with another substring.
.rfind(): Finds the last occurrence of a specified substring and returns the starting index.
.rindex(): Locates the highest index of the substring within a string variable.
.rjust(): Adds padding to the left of the given string.
.rpartition(): Used to split a string into three parts based on a specified separator.
.rsplit(): Splits a string into a list of substrings from the right end of the string based on a specified delimiter.
.rstrip(): Removes trailing characters from a string.
.split(): Converts a string to a list. It takes a specified delimiter and a maximum number of items to split as optional parameters.
.splitlines(): Used to split a multi-line string into a list of lines.
.startswith(): Checks whether or not a string starts with a given value.
.strip(): Eliminates any trailing spaces at the beginning and end of a string. Specific characters can be passed in as an argument to be removed instead.
.swapcase(): Takes a string and returns a copy of that string in which all lowercase letters are uppercase, and all uppercase letters are lowercase. Numbers and symbols are not changed.
.title(): Takes in a string and returns a copy of the string formatted in the title case: each word in the string is capitalized.
.translate(): Replaces characters in a string based on a mapping table.
.upper(): Takes a string, and returns a copy of that string in which all letters are uppercase. Numbers and symbols are not changed.
.zfill(): Returns a string with zeros padding the left side based on the integer given.
maketrans(): Returns a transition table based on the given strings.