Python course: Strings

1. Replicating strings
2. Escape sequences
3. Raw strings
4. Slicing
5. Some methods

Strings are used to represent text in Python. Any of these syntaxes are valid strings:

name_1 = 'Stanley Hudson'
name_2 = "Stanley Hudson"
name_3 = """
Stanley
Hudson
"""
name_4 = """
Stanley Hudson
"""

name_3 and name_4: these are ways of representing multi-line strings.

In more realistic scenarios, you are more likely to use strings composed by regular text plus other values obtained from variables. Let's say you want a string to greet someone based on their name:

This process is also known as “string interpolation”.

name = "Angela"
animal = "cat"
greeting_1 = f"Welcome, {name}"
greeting_2 = "Welcome, " + name
greeting_3 = "Welcome, %s" % name
greeting_4 = "Welcome, {}. Are you a {} person ?".format(name,
animal)
print(greeting_1) # => "Welcome, Angela"
print(greeting_2) # => "Welcome, Angela"
print(greeting_3) # => "Welcome, Angela"
print(greeting_4) # => "Welcome, Angela. Are you a cat person ?

Some explanation about these string variables:

greeting_1
This is the convention adopted throughout this series of articles, since I find it more convenient to use and readable. Also, it’s the most modern approach.

Notice the “f” must be placed right before the beginning of the string.

greeting_2
Notice the “+” sign. When dealing with strings, it means concatenation (joining). If you use it with numbers, such as integers or floats, it means a mathematical sum. This ability to perform different actions according to how it’s used is called polymorphism (poly=many, morph=form). So, in Python, the “+” sign is polymorphic. You will see about numbers in the Numbers article.

greeting_3
The “%s” stands for “string”. If the name variable was an integer, for
instance, then “%i” should be used instead of “%s”.

greeting_4
The format method was used here (you’ll learn more about this in the Classes article), and the contents inside the curly brackets “{}” were replaced by the name and animal variables, respectively.

Replicating strings

An interesting use case for strings is being able to replicate it multiple times by using the * operator, the same one used for multiplying numbers.

branch = "Buffalo" 
many_times = branch * 3
print(many_times) # => "BuffaloBuffaloBuffalo"

Escape sequences

These are special characters that can be used in strings to provide some additional features. They are denoted by a backslash " \ ", followed by the character:

Examples:

print("This is a\ttabbed string.")
print("This is a\nstring with a new line.")
print("This is a string with a backslash: \\")
print('This is a string with a single quote: \'')
print("This is a string with a double quote: \"")

Output seen in the command-line:

This is a       tabbed string.
This is a
string with a new line.
This is a string with a backslash: \
This is a string with a single quote: '
This is a string with a double quote: "«

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Raw strings

In certain situations, you may want to actually use these escaped characters demonstrated above. A common use case is for file paths on Windows computers, which include the backslash "\" character. This can be accomplished by appending "r" right before the beginning of a string:

jan_photo = r"C:\Users\Michael\princess_of_jamaica.jpg"
print(jan_photo) # => C:\Users\Michael\princess_of_jamaica.jpg

Slicing strings

You can get parts of a string by accessing their indexes. In Python, we start counting indexes/positions at 0, and negative indexes are counted backwards, from end to start. The concept of indexes and slicing will be covered in the Lists article.

name = "RYAN"

print(name[0]) # => R
print(name[1]) # => Y
print(name[2]) # => A
print(name[3]) # => N
print(name[-1]) # => N
print(name[1:3]) # => YA

Some string methods

Here are some usages of popular methods available for strings. Check them at https://docs.python.org/3/library/stdtypes.html#str.capitalize. The concept of "method" will be explained in the Classes article. For now, keep in mind they are a way of providing extra-capabilities to objects such as strings in this case. For example, turning a string into uppercase or lowercase.

name = "jim"

print("jim".upper())  # => JIM
print(name.capitalize())  # => Jim
print("JIM".lower()) # => jim

# how many times 'f' is repeated in 'Buffalo'
print("Buffalo".count("f"))  # => 2

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