Python Strings
Strings
Strings in python are surrounded by either single quotation marks, or double quotation marks.
'hello' is the same as "hello".
You can display a string literal with the print() function:
Example
print("Hello")
print('Hello')
Quotes Inside Quotes
You can use quotes inside a string, as long as they don't match the quotes surrounding the string:
Example
print("It's alright")
print("He is called 'Johnny'")
print('He is called "Johnny"')
Assign String to a Variable
Assigning a string to a variable is done with the variable name followed by an equal sign and the string:
Example
a = "Hello"
print(a)
Multiline Strings
You can assign a multiline string to a variable by using three quotes:
Example
You can use three double quotes:
a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."""
print(a)
Strings are Arrays
Like many other popular programming languages, strings in Python are arrays of unicode characters.
However, Python does not have a character data type, a single character is simply a string with a length of 1.
Square brackets can be used to access elements of the string.
Example
Get the character at position 1 (remember that the first character has the position 0):
a = "Hello, World!"
print(a[1])
Looping Through a String
Since strings are arrays, we can loop through the characters in a string, with a for loop.
Example
Loop through the letters in the word "banana":
for x in "banana":
print(x)
String Length
To get the length of a string, use the len() function.
Example
The len() function returns the length of a string:
a = "Hello, World!"
print(len(a))
Check String
To check if a certain phrase or character is present in a string, we can use the keyword in.
Example
Check if "free" is present in the following text:
txt = "The best things in life are free!"
print("free" in txt)
Python - Slicing Strings
Slicing
You can return a range of characters by using the slice syntax.
Specify the start index and the end index, separated by a colon, to return a part of the string.
Example
Get the characters from position 2 to position 5 (not included):
b = "Hello, World!"
print(b[2:5])
Note: The first character has index 0.
Slice From the Start
By leaving out the start index, the range will start at the first character:
Example
Get the characters from the start to position 5 (not included):
b = "Hello, World!"
print(b[:5])
Slice To the End
By leaving out the end index, the range will go to the end:
Example
Get the characters from position 2, and all the way to the end:
b = "Hello, World!"
print(b[2:])
Negative Indexing
Use negative indexes to start the slice from the end of the string:
Example
Get the characters:
From: "o" in "World!" (position -5)
To, but not included: "d" in "World!" (position -2):
b = "Hello, World!"
print(b[-5:-2])
Python - Modify Strings
Python has a set of built-in methods that you can use on strings.
Upper Case
Example
The upper() method returns the string in upper case:
a = "Hello, World!"
print(a.upper())
Lower Case
Example
The lower() method returns the string in lower case:
a = "Hello, World!"
print(a.lower())
Remove Whitespace
Whitespace is the space before and/or after the actual text, and very often you want to remove this space.
Example
The strip() method removes any whitespace from the beginning or the end:
a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"
Replace String
Example
The replace() method replaces a string with another string:
a = "Hello, World!"
print(a.replace("H", "J"))
Split String
The split() method returns a list where the text between the specified separator becomes the list items.
Example
The split() method splits the string into substrings if it finds instances of the separator:
a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']
Learn more about Lists in our Python Lists chapter.
Python - String Concatenation
String Concatenation
To concatenate, or combine, two strings you can use the + operator.
Example
Merge variable a with variable b into variable c:
a = "Hello"
b = "World"
c = a + b
print(c)
Example
To add a space between them, add a " ":
a = "Hello"
b = "World"
c = a + " " + b
print(c)
Python - Format - Strings
String Format
As we learned in the Python Variables chapter, we cannot combine strings and numbers like this:
Example
age = 36
#This will produce an error:
txt = "My name is John, I am " + age
print(txt)
But we can combine strings and numbers by using f-strings or the format() method!
F-Strings
F-String was introduced in Python 3.6, and is now the preferred way of formatting strings.
To specify a string as an f-string, simply put an f in front of the string literal, and add curly brackets {} as placeholders for variables and other operations.
Example
Create an f-string:
age = 36
txt = f"My name is John, I am {age}"
print(txt)
Placeholders and Modifiers
A placeholder can contain variables, operations, functions, and modifiers to format the value.
Example
Add a placeholder for the price variable:
price = 59
txt = f"The price is {price} dollars"
print(txt)
A placeholder can include a modifier to format the value.
A modifier is included by adding a colon : followed by a legal formatting type, like .2f which means fixed point number with 2 decimals:
Example
Display the price with 2 decimals:
price = 59
txt = f"The price is {price:.2f} dollars"
print(txt)
A placeholder can contain Python code, like math operations:
Example
Perform a math operation in the placeholder, and return the result:
txt = f"The price is {20 * 59} dollars"
print(txt)
Python - Escape Characters
Escape Character
To insert characters that are illegal in a string, use an escape character.
An escape character is a backslash \ followed by the character you want to insert.
An example of an illegal character is a double quote inside a string that is surrounded by double quotes:
Example
You will get an error if you use double quotes inside a string that is surrounded by double quotes:
txt = "We are the so-called "Vikings" from the north."To fix this problem, use the escape character \":
Example
The escape character allows you to use double quotes when you normally would not be allowed:
txt = "We are the so-called \"Vikings\" from the north."Escape Characters
Other escape characters used in Python:
| Code | Result | Try it |
|---|---|---|
| \' | Single Quote | |
| \\ | Backslash | |
| \n | New Line | |
| \t | Tab | |
| \r | Carriage Return | |
| \b | Backspace | |
| \f | Form Feed | |
| \ooo | Octal Value | |
| \xhh | Hex value |