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Strings

Strings in Python are sequences of characters used to store text. They are one of the most versatile primitive types. They are 0-indexed and their length can be found using len(string).

Creating Strings​

We can use single or double quotes for strings. Triple quotes are used for multi-line strings.

name = "Alice"
greeting = 'Hello'
multi_line = """This is a
long string."""

print(name, greeting)
Alice Hello

Immutability​

Strings are immutable—we cannot change a character in place. If we're coming from C, we might be used to changing an array in place; in Python, we have to create a new string instead.

fruit = "Apple"
# fruit[0] = "B"  # This would cause a TypeError

# Instead, create a new one
new_fruit = "B" + fruit[1:]
print(new_fruit)
Bpple

Common String Methods​

Python has hundreds of built-in methods for strings to handle common formatting and transformation tasks.

text = "  Python is fun!  "

print(text.lower())      # lowercase
print(text.upper())      # uppercase
print(text.strip())      # Remove whitespace from ends
print(text.replace("fun", "powerful"))
  python is fun!
  PYTHON IS FUN!
Python is fun!
  Python is powerful!

Slicing Syntax​

Slicing uses the [start:stop:step] format. Remember that the "stop" number is exclusive (it stops before that index).

pie = "ApplePie"

# Basic slicing: [start:stop]
print(pie[2:6])     # 'pleP' (starts at 2, stops before 6)

# Shortcuts
print(pie[:5])      # 'Apple' (omitting start defaults to 0)
print(pie[5:])      # 'Pie' (omitting stop goes to the end)
print(pie[-3:])     # 'Pie' (counting from the end)

# Reversing a string
# We can use a negative step to traverse the string backwards.
print(pie[::-1])

Output:

pleP
Apple
Pie
Pie
eiPelppA

Splitting and Unpacking​

Use .split() to break a string into a list. Use unpacking to assign parts directly to variables instead of indexing multiple times.

# Pythonic: Split once and assign both variables
name, age_str = "google-12".split('-')
age = int(age_str)

print(name, age)
google 12

Direct Iteration​

Don't use an index counter to look at every character. Python strings are iterable collections, so we can loop through them directly.

# The clean way to look at every character
for char in "ABC":
    print(char)
A
B
C