§ cheat sheet

Python Strings

Indexing, case and whitespace, searching, split/join, f-string formatting and the byte-level bits.

45 snippets · 6 sections · Python 3.12Related lesson: Strings →

The snippets assume

s = "Hello, World"

Create and inspect

Try it in the playground →

```
len(s)
```
Number of characters (12).
```
s[0], s[-1]
```
First and last character; negative indexes count from the end.
```
s[7:12]
```
Slice from index 7 up to, not including, 12 → 'World'.
```
s[::-1]
```
Reversed copy; strings are immutable, so every method returns a new one.
```
"py" * 3
```
Repeat → 'pypypy'.
```
"Hello, " + "World"
```
Concatenate. For many pieces prefer join or an f-string.
```
str(42), repr("hi")
```
Any object to text; repr gives the quoted, debug form.
```
"tab\there\nnew line"
```
\t tab, \n newline, \\ backslash, \" quote.
```
r"C:\new\dir"
```
Raw string: backslashes are kept literally (use for regex and Windows paths).

Case and whitespace

Try it in the playground →

```
s.upper(), s.lower()
```
'HELLO, WORLD', 'hello, world'.

"hello world".title(), "hello".capitalize()

'Hello World'; 'Hello' (first letter only).

```
"Straße".casefold() == "strasse"
```
Aggressive lowercase for case-insensitive comparison.
```
"  pad  ".strip()
```
Remove whitespace at both ends; lstrip / rstrip for one side.
```
"xxhixx".strip("x")
```
Strip a set of characters instead of whitespace.
```
"7".zfill(3)
```
Left-pad with zeros → '007'.

"hi".center(6, "*"), "hi".ljust(5, "."), "hi".rjust(5)

'**hi**', 'hi...', ' hi'.

Search and test

Try it in the playground →

```
"World" in s
```
Substring test → True.
```
s.find("o"), s.rfind("o")
```
First / last index, or -1 when absent.
```
s.index("o")
```
Like find but raises ValueError when absent.
```
s.count("l")
```
Non-overlapping occurrences → 3.
```
s.startswith("He"), s.endswith(("d", "x"))
```
Prefix / suffix test; a tuple means any of them.

"abc".isalpha(), "123".isdigit(), "a1".isalnum()

Only letters / only digits / letters or digits.

"   ".isspace(), "Hello World".istitle(), "ABC".isupper()

Whitespace only / title case / all caps.

```
"3.5".isdigit(), "35".isdigit()
```
→ False, True. To test for a number, use try: float(x) except ValueError.

Split, join, replace

Try it in the playground →

```
"a,b,c".split(",")
```
→ ['a', 'b', 'c'].
```
"a  b\tc".split()
```
No argument: split on any whitespace run and drop empties.
```
"a,b,c".split(",", 1)
```
At most one split → ['a', 'b,c']; rsplit works from the right.
```
"key=value".partition("=")
```
→ ('key', '=', 'value'); always a 3-tuple.
```
"one\ntwo\n".splitlines()
```
→ ['one', 'two']; handles \n, \r\n and drops the trailing empty.
```
", ".join(["a", "b", "c"])
```
Join an iterable of strings → 'a, b, c'. Items must already be str.
```
s.replace("l", "L"), s.replace("l", "L", 1)
```
Replace all, or only the first n occurrences.

"Hello, World".removeprefix("Hello, ").removesuffix("ld")

→ 'Wor' (3.9+); no error when the affix is absent.

Format

Try it in the playground →

```
f"{2 + 2} is {'four'}"
```
Any expression inside the braces.
```
f"{3.14159:.2f}"
```
Two decimals → '3.14'.
```
f"{1234567:,}", f"{1234567:_}"
```
Thousands separator → '1,234,567' / '1_234_567'.
```
f"[{42:>6}] [{42:<6}] [{42:^6}]"
```
Right / left / centre align in width 6.
```
f"{0.256:.1%}"
```
Percentage → '25.6%'.

f"{255:x} {255:X} {255:b} {255:08b} {255:o}"

Hex, HEX, binary, zero-padded binary, octal.

```
x = 5; f"{x=}"
```
Debug form → 'x=5' (3.8+).
```
"{} and {name}".format("a", name="b")
```
str.format: positional and named fields.
```
"%s: %d" % ("count", 3)
```
printf style; still common in logging calls.

Bytes and code points

Try it in the playground →

```
ord("A"), chr(65)
```
Character ↔ code point (65).
```
"é".encode("utf-8")
```
→ b'\xc3\xa9'; bytes is what files and sockets carry.
```
b"\xc3\xa9".decode("utf-8")
```
Bytes back to str → 'é'.
```
"abc".translate(str.maketrans("ab", "xy"))
```
Per-character mapping → 'xyc'; pass a 3rd arg to delete chars.

Want the topic explained, not just listed? The Strings lesson walks through it with graded exercises. Preparing for interviews? See the interview prep track.

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