Python String Methods Cheat Sheet

Quick reference for Python's str type — creating, slicing, searching, transforming, formatting. Strings are immutable: every method returns a new string. For the full tutorial, see Strings.

Creating

python

a = 'single'
b = "double"
c = """triple
spans lines"""
d = r"C:\Users\raw\no\escapes"          # raw — backslashes literal
e = b"bytes"                            # bytes, not str
f = "concat" + "enation"
g = "repeat" * 3                        # 'repeatrepeatrepeat'
h = str(42)                             # from anything: '42'

Indexing & Slicing

python

s = "python"
s[0]        # 'p'      first
s[-1]       # 'n'      last
s[1:4]      # 'yth'    [start:stop)
s[:3]       # 'pyt'
s[3:]       # 'hon'
s[::2]      # 'pto'    every 2nd
s[::-1]     # 'nohtyp' reverse
len(s)      # 6

Inspecting

Method	What it does	Example	Returns
`len(s)`	Length	`len("abc")`	`3`
`sub in s`	Membership	`"th" in "python"`	`True`
`s.count(sub)`	Occurrences	`"banana".count("a")`	`3`
`s.find(sub)`	First index or -1	`"hello".find("l")`	`2`
`s.rfind(sub)`	Last index or -1	`"hello".rfind("l")`	`3`
`s.index(sub)`	First index, raises ValueError	`"hello".index("z")`	`ValueError`
`s.startswith(p)`	Prefix check	`"file.py".startswith("file")`	`True`
`s.endswith(p)`	Suffix check	`"file.py".endswith(".py")`	`True`
`s.isdigit()`	All digits 0-9	`"123".isdigit()`	`True`
`s.isalpha()`	All letters	`"abc".isalpha()`	`True`
`s.isalnum()`	Letters or digits	`"abc123".isalnum()`	`True`
`s.isspace()`	All whitespace	`" \n".isspace()`	`True`
`s.islower()` / `isupper()`	Case check	`"abc".islower()`	`True`

Case

Method	Example	Returns
`s.upper()`	`"hi".upper()`	`'HI'`
`s.lower()`	`"HI".lower()`	`'hi'`
`s.title()`	`"hi there".title()`	`'Hi There'`
`s.capitalize()`	`"hello world".capitalize()`	`'Hello world'`
`s.swapcase()`	`"Hi There".swapcase()`	`'hI tHERE'`
`s.casefold()`	`"Straße".casefold()`	`'strasse'` (aggressive lower, use for compare)

Trimming

python

"  hi  ".strip()        # 'hi'
"  hi  ".lstrip()       # 'hi  '
"  hi  ".rstrip()       # '  hi'
"xxhixx".strip("x")     # 'hi'        any char in set
"www.site.com".strip("wcom.")  # 'site' — chars, not substring!

Splitting & Joining

Method	Example	Returns
`s.split(sep)`	`"a,b,c".split(",")`	`['a','b','c']`
`s.split()`	`" a b\tc ".split()`	`['a','b','c']` (any whitespace)
`s.split(sep, n)`	`"a,b,c".split(",", 1)`	`['a','b,c']`
`s.rsplit(sep, n)`	`"a,b,c".rsplit(",", 1)`	`['a,b','c']`
`s.splitlines()`	`"a\nb\n".splitlines()`	`['a','b']`
`s.partition(sep)`	`"key=val".partition("=")`	`('key','=','val')`
`sep.join(iter)`	`",".join(['a','b'])`	`'a,b'`

Replacing

python

"hello".replace("l", "L")            # 'heLLo'
"hello".replace("l", "L", 1)         # 'heLlo'   max 1
tbl = str.maketrans("aeiou", "AEIOU")
"hello".translate(tbl)               # 'hEllO'
"hello".translate(str.maketrans("", "", "aeiou"))  # 'hll' — delete

Formatting

python

name, n = "Ada", 42
f"{name} is {n}"                # f-string (preferred, 3.6+)
"{} is {}".format(name, n)      # .format()
"%s is %d" % (name, n)          # legacy % — avoid in new code

Format spec mini-reference (`f"{value:spec}"`)

Spec	Meaning	Example	Output
`.2f`	2 decimal places	`f"{3.14159:.2f}"`	`'3.14'`
`,`	Thousands separator	`f"{1000000:,}"`	`'1,000,000'`
`>10`	Right-align width 10	`f"{'hi':>10}"`	`' hi'`
`<10`	Left-align	`f"{'hi':<10}"`	`'hi '`
`^10`	Centre	`f"{'hi':^10}"`	`' hi '`
`0>3`	Pad with zeros	`f"{7:0>3}"`	`'007'`
`e`	Scientific	`f"{12345:.2e}"`	`'1.23e+04'`
`%`	Percent	`f"{0.5:.0%}"`	`'50%'`
`b/o/x`	Binary/oct/hex	`f"{255:x}"`	`'ff'`

See F-Strings for the full guide.

Encoding

python

"café".encode()             # b'caf\xc3\xa9'      default utf-8
"café".encode("utf-16")
b'caf\xc3\xa9'.decode()     # 'café'

# Escape sequences
"\n"   # newline
"\t"   # tab
"\\"   # literal backslash
"\""   # literal quote
"é"  # é (unicode)

Common Patterns

python

# Slug
text.strip().lower().replace(" ", "-")

# Pad
str(7).zfill(4)                  # '0007'
f"{7:0>4}"                       # '0007'

# Reverse
s[::-1]

# Join list of ints to CSV
",".join(str(x) for x in [1,2,3])   # '1,2,3'

# Strip extension
"report.pdf".removesuffix(".pdf")   # 'report'   (3.9+)
"file_log".removeprefix("file_")    # 'log'      (3.9+)

# Check multiple suffixes
name.endswith((".jpg", ".png", ".gif"))

+ setup added so this can run · defines s, name, text

# Lightweight mock for objects whose attributes/methods aren't critical
class _AutoMock:
    def __init__(self, name='mock'): self._name = name
    def __getattr__(self, k): return _AutoMock(self._name + '.' + k)
    def __call__(self, *a, **kw):
        print('-> ' + self._name + '() called')
        return _AutoMock(self._name + '()')
    def __repr__(self): return '<mock ' + self._name + '>'
    def __str__(self): return '<mock ' + self._name + '>'
    def __bool__(self): return True
    def __iter__(self): return iter([])
    def __len__(self): return 0
    def __getitem__(self, k): return _AutoMock(self._name + '[...]')
    def __setitem__(self, k, v): pass
    def __enter__(self): return self
    def __exit__(self, *a): return False
    async def __aenter__(self): return self
    async def __aexit__(self, *a): return False
    def __add__(self, o): return self
    def __radd__(self, o): return self
    def __sub__(self, o): return self
    def __mul__(self, o): return self
    def __rmul__(self, o): return self
    def __truediv__(self, o): return self
    def __eq__(self, o): return isinstance(o, _AutoMock)
    def __hash__(self): return hash(self._name)
    def __lt__(self, o): return True
    def __le__(self, o): return True
    def __gt__(self, o): return False
    def __ge__(self, o): return False
    def __mro_entries__(self, bases): return (object,)

s = ["alpha", "beta", "gamma"]
name = _AutoMock('name')
text = _AutoMock('text')

Common Errors

Error	Cause	Fix
`TypeError: 'str' object does not support item assignment`	`s[0] = "X"`	Strings are immutable — build new: `"X" + s[1:]`. See full page
`AttributeError: 'str' object has no attribute 'append'`	Treating string like list	Use `+`, `+=`, or `"".join(parts)`
`ValueError: substring not found`	`.index(x)` when `x` absent	Use `.find()` (returns -1) or guard with `in`
`TypeError: can only concatenate str (not "int") to str`	`"x" + 5`	Convert: `"x" + str(5)` or use f-string
`UnicodeDecodeError`	Wrong codec on `.decode()`	Specify correct encoding, e.g. `.decode("latin-1")`

1 · The lesson

Creating

Indexing & Slicing

Inspecting

Case

Trimming

Splitting & Joining

Replacing

Formatting

Format spec mini-reference (`f"{value:spec}"`)

Encoding

Common Patterns

Common Errors

See Also

Practice this

Python String Methods Cheat Sheet

Creating

Indexing & Slicing

Inspecting

Case

Trimming

Splitting & Joining

Replacing

Formatting

Format spec mini-reference (f"{value:spec}")

Encoding

Common Patterns

Common Errors

See Also

Format spec mini-reference (`f"{value:spec}"`)