Strings

Strings are sequences of characters enclosed in quotes. A string literal is created by placing characters between quotes:

single_quoted = 'This uses single quotes.'
double_quoted = "This uses double quotes."
print(single_quoted)  # Output: This uses single quotes.

Single and double quotes are interchangeable. Having both allows us to embed one type inside the other:

message = "It's a lovely day"      # Apostrophe inside double quotes
quote = 'He said "hello"'          # Double quotes inside single quotes
nested = "'Python'"                # Single quotes as part of the string

Multi-line strings

For strings spanning multiple lines, use triple quotes (''' or """):

multi_line = '''This string
spans multiple
lines.'''

also_valid = """Triple quotes work
for multi-line text."""

single_line_triple_quote = """This is also valid"""

Triple quotes preserve line breaks in the output.

Escape sequences

To include special characters in a string, use the backslash (\) as an escape character. When printed, these sequences produce:

Embedding quotes

Use double quotes to include an apostrophe, or single quotes to include double quotes:

print("It's raining")       # Apostrophe inside double quotes
print('She said "hello"')   # Double quotes inside single quotes

Output:

It's raining
She said "hello"

Escape sequences

Use backslash to insert special characters like newlines, tabs, and literal backslashes:

print("Line 1\nLine 2")     # \n = newline
print("Name:\tAlice")       # \t = tab
print("C:\\Users\\name")    # \\ = literal backslash
print('It\'s also valid')   # \' = apostrophe in single-quoted string

Output:

Line 1
Line 2
Name:	Alice
C:\Users\name
It's also valid

Notice that \n, \t, \\, and \' don't appear literally in the output - they produce a newline, tab, single backslash, and apostrophe respectively.

Two basic string operations are concatenation and repetition.

Concatenation joins strings end-to-end using the + operator:

"Hello" + "World"  # Result: "HelloWorld"

Repetition repeats a string using the * operator with an integer:

"echo" * 3  # Result: "echoechoecho"

Building a full name

first_name = "John"
last_name = "Doe"
full_name = first_name + last_name
print(full_name)  # Output: JohnDoe

The names are joined directly with no space between them.

Adding a space

To separate the names, we concatenate an extra space string:

full_name = first_name + " " + last_name
print(full_name)  # Output: John Doe

Repeating strings

word = "echo"
repeated = word * 3
print(repeated)  # Output: echoechoecho

Combining both

We can use concatenation and repetition together:

result = "ha" * 3 + "!"
print(result)  # Output: hahaha!

Strings have built-in methods we can call using dot notation: string.method_name(). Each method returns a new string (the original is unchanged).

Case conversion

• .lower() - converts all characters to lowercase
• .upper() - converts all characters to uppercase

Whitespace and characters

• .strip() - removes leading and trailing whitespace (or specified characters)

Searching

• .find(substring) - returns the index of the first occurrence, or -1 if not found
• .startswith(substring) - returns True if the string starts with the substring
• .endswith(substring) - returns True if the string ends with the substring

Replacing

• .replace(old, new) - replaces all occurrences of old with new

Case conversion

text = "Hello World!"
print(text.lower())  # Output: hello world!
print(text.upper())  # Output: HELLO WORLD!

Stripping whitespace

text = "   Hello World!   "
print(text.strip())  # Output: Hello World!

We can also strip specific characters:

text = "!!Hello World!!"
print(text.strip('!'))  # Output: Hello World

Note: .strip() only removes from the start and end, not the middle.

Finding substrings

text = "Hello World"
print(text.find("World"))  # Output: 6
print(text.find("Python")) # Output: -1

Checking start and end

text = "Hello World"
print(text.startswith("Hello"))  # Output: True
print(text.endswith("World"))    # Output: True
print(text.endswith("world"))  # Output: False (case-sensitive)

Replacing substrings

text = "Hello, World"
print(text.replace("World", "Python"))  # Output: Hello, Python