Strings

Strings are a sequence of alphanumeric and ascii characters.

# Strings are created with " or '
print("This is a string.")
print('This is also a string.')

# Strings can be added too
print("Hello " + "world!")  # => "Hello world!"
# String literals (but not variables) can be concatenated without using '+'
print("Hello " "world!")    # => "Hello world!"

We can find the length of a string with the len keyword

print(len("This is a string")) # => 16

Once we talk more about variables the following becomes really useful

# Since Python 3.6, you can use f-strings or formatted string literals.
name = "Reiko"
print(f"She said her name is {name}.")  # => "She said her name is Reiko"

# Any valid Python expression inside these braces is returned to the string.
name = "Reiko"
print(f"{name} is {len(name)} characters long.")  # => "Reiko is 5 characters long."

if we want to include the literal character " in a string, we can use the escape character \ like the following

print("these are \"quotes\" and are cool!")

here is a list of different characters that would need to be escaped, try them out

• \' single quote, if you are using ' to quote
• \\ the backslash character
• \n new line
• \r carriage return
• \t tab
• \b backspace
• \f form feed

print("edit me and try some of the escape characters!")

Methods of strings

We can call a couple functions on things of string type

# str.index(n) returns the index of the first found substring `n` in a string,
# raises a ValueError if index does not exist. (We will talk more exceptions in a later section).
str = 'robor'
print(str.index('ro')) # => 0
print(str[0])       # => r

print(str.index('bor')) # => 2
print(str[2])       # => b

# str.isalnum() returns 'True' if characters in the string are alphanumeric
# (i.e. is a number of letter) and there is at least one character.
str1 = 'robor123'
str2 = '""'
str3 = '' # strings can have no characters! (this is an empty string)

print(str1.isalnum()) # => True
print(str2.isalnum()) # => False
print(str3.isalnum()) # => False

# str.upper() returns returns a copy of the string with all the cased characters converted to uppercase.
str1 = 'ww1757'
print(str1.upper())) # => 'WW1757'
print(str1) # => 'ww1757'
# note the original string is unaffected as str.upper() returns a copy!

# str.lower() returns returns a copy of the string with all the cased characters converted to lowercase.
str1 = 'WestWood1757'
print(str1.lower())) # => 'westwood1757'
print(str1) # => 'WestWood1757'
# note the original string is unaffected as str.lower() returns a copy!

Python has powerful string manipulation methods already built into the language. You should take advantadge of these where possible. For an exhaustive list, check out the official Python docs.

After this, try out Challenge 1!

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