Python String Methods: The Complete Reference

text = "hello World"

text.upper()          # 'HELLO WORLD'
text.lower()          # 'hello world'
text.capitalize()     # 'Hello world'
text.title()          # 'Hello World'
text.swapcase()       # 'HELLO wORLD'

text = "Hello123"

text.isalpha()        # False (has digits)
text.isdigit()        # False (has letters)
text.isalnum()        # True (letters + digits)
text.islower()        # False
text.isupper()        # False
text.isspace()        # False
text.startswith("Hel")  # True
text.endswith("123")    # True

text = "hello world hello"

text.find("world")        # 6 (index of first match)
text.find("xyz")          # -1 (not found)
text.index("world")       # 6 (like find, but raises ValueError)
text.rfind("hello")       # 12 (search from right)
text.count("hello")       # 2

"in" in text              # True (in operator)

text = "  hello world  "

text.strip()          # 'hello world' (remove leading/trailing whitespace)
text.lstrip()         # 'hello world  ' (left only)
text.rstrip()         # '  hello world' (right only)
text.replace("world", "Python")  # '  hello Python  '

"a,b,c".replace(",", " | ")      # 'a | b | c'

# Split
"a,b,c".split(",")          # ['a', 'b', 'c']
"a b c".split()             # ['a', 'b', 'c'] (splits on any whitespace)
"a,b,c".split(",", maxsplit=1)  # ['a', 'b,c']

"line1\nline2\nline3".splitlines()  # ['line1', 'line2', 'line3']

# Join
", ".join(["a", "b", "c"])  # 'a, b, c'
"".join(["h", "e", "l", "l", "o"])  # 'hello'
" -> ".join(["a", "b", "c"])  # 'a -> b -> c'

text = "hello"

text.center(11)       # '   hello   '
text.ljust(10)        # 'hello     '
text.rjust(10)        # '     hello'
text.zfill(8)         # '000hello' (pad with zeros)

"42".zfill(5)         # '00042'

"file.txt.txt".strip(".txt")        # 'file' (removes . t x)
"file.txt.txt".removesuffix(".txt") # 'file.txt' (Python 3.9+)
"file.txt.txt".removeprefix("file") # '.txt.txt' (Python 3.9+)

"  hello  ".strip(" h")            # 'ello'

name = "Alice"
age = 30
f"{name} is {age} years old"        # 'Alice is 30 years old'
f"{name:>10}"                        # '     Alice' (right align)
f"{name:<10}"                        # 'Alice     ' (left align)
f"{name:^10}"                        # '  Alice   ' (center)
f"{age:03d}"                         # '030' (zero pad)
f"{3.14159:.2f}"                     # '3.14' (2 decimal places)
f"{1000:,}"                          # '1,000' (thousands separator)
f"{0.25:.1%}"                        # '25.0%' (percentage)

"{} is {} years old".format("Alice", 30)
"{name} is {age} years old".format(name="Alice", age=30)
"{1} is {0} years old".format(30, "Alice")

"hello".encode("utf-8")         # b'hello'
"hello".encode("utf-16")        # b'\xff\xfeh\x00e\x00...'

ord("A")                        # 65 (Unicode code point)
chr(65)                         # 'A'

# Remove punctuation
import string
"hello, world!".translate(str.maketrans("", "", string.punctuation))
# 'hello world'

# Check if string is a number
"42".isdigit()                           # True
"42.5".isdigit()                         # False
"42.5".replace(".", "").isdigit()        # True (hacky)

# Better: try parsing
def is_number(s):
    try:
        float(s)
        return True
    except ValueError:
        return False

# Split lines preserving line endings
"a\nb\nc".splitlines(keepends=True)     # ['a\n', 'b\n', 'c']

# Reverse a string
"hello"[::-1]                           # 'olleh'