String Manipulation — Python Basics

String methods

python

text = "  Hello, World!  "

# Case
text.upper()         # "  HELLO, WORLD!  "
text.lower()         # "  hello, world!  "
text.title()         # "  Hello, World!  "
text.capitalize()    # "  hello, world!  " (only first char)

# Whitespace
text.strip()         # "Hello, World!"  (both ends)
text.lstrip()        # "Hello, World!  " (left only)
text.rstrip()        # "  Hello, World!" (right only)

# Searching
text.find("World")      # 9 (index of first match, -1 if not found)
text.count("l")         # 3
text.startswith("  H")  # True
text.endswith("!  ")    # True
"World" in text         # True

# Modifying (returns new string)
text.replace("World", "Python")   # "  Hello, Python!  "
text.replace(" ", "", 1)          # replaces only first occurrence

# Splitting and joining
"a,b,c".split(",")           # ["a", "b", "c"]
"Hello World".split()        # ["Hello", "World"] (splits on whitespace)
", ".join(["a", "b", "c"])   # "a, b, c"

# Padding
"42".zfill(5)       # "00042"
"left".ljust(10)    # "left      "
"right".rjust(10)   # "     right"

f-strings — the best way to format strings

python

name   = "Nelson"
score  = 98.754
courses = 12

# Basic embedding
f"Hello, {name}!"              # "Hello, Nelson!"

# Expressions inside {}
f"2 + 2 = {2 + 2}"             # "2 + 2 = 4"
f"Upper: {name.upper()}"       # "Upper: NELSON"

# Formatting numbers
f"Score: {score:.2f}"          # "Score: 98.75"
f"Score: {score:.0f}%"         # "Score: 99%"
f"Courses: {courses:,}"        # "Courses: 12"
f"Pi: {3.14159:.3f}"           # "Pi: 3.142"
f"Hex: {255:#x}"               # "Hex: 0xff"

# Alignment
f"{'left':<10}|{'right':>10}"  # "left      |     right"

# Debug (Python 3.8+)
f"{score=}"   # "score=98.754" — print name and value together