Strings#

Strings in Python are sequences of characters enclosed in single quotes ' ' or double quotes " ".

String Operators#

Operator	Description
`+`	Concatenation — joins two strings
`*`	Repetition — repeats a string n times
`[ : ]`	Slice — extracts a substring by index range
`in`	Membership — returns True if a character exists in the string

Indexing and Slicing#

Indexes start at 0 from the left and -1 from the right:

 +---+---+---+---+---+
 | H | e | l | l | o |
 +---+---+---+---+---+
 0   1   2   3   4   5
-5  -4  -3  -2  -1

>>> text = "Fortunately"
>>> text[0:4]
'Fort'
>>> text[5:-2]
'nate'

Built-in String Functions#

Function	Description
`ord('A')`	Get the Unicode code point for a character
`chr(65)`	Get the character for a Unicode code point

String Methods#

Method	Description
`str.lower()`	Convert to lowercase
`str.upper()`	Convert to uppercase
`str.capitalize()`	Capitalize the first letter
`str.split("sep")`	Split into a list using separator
`str.find("sub", start, end)`	Find substring; returns index or -1
`str.strip()`	Remove leading/trailing whitespace
`str.replace("old", "new")`	Replace occurrences of a substring
`"sep".join(list)`	Join list items into a string with separator
`str.encode("utf-8")`	Encode string to bytes

>>> var1 = "Hello"
>>> var2 = "world"
>>> print(var1 + " " + var2)
Hello world
>>> "spam eggs".split(" ")
['spam', 'eggs']

String Formatting#

Python offers three formatting approaches: % operator (legacy), .format(), and f-strings (recommended).

Formatting Types#

Type	Description
`s`	String
`d`	Integer
`f`	Floating-point decimal
`e`	Scientific notation
`c`	Single character (from integer code point)

Basic Examples#

# % operator (legacy)               # .format()                          # f-string (recommended)
>>> "Name: %s, age: %d" % ('Zara', 45)
>>> "Name: {}, age: {}".format('Zara', 45)
>>> name, age = 'Zara', 45
>>> f"Name: {name}, age: {age}"
'Name: Zara, age: 45'

Width and Fill#

>>> f"{'Foo':>5}"       # Right-align in 5 characters
'  Foo'
>>> f"{'Foo':<5}"       # Left-align in 5 characters
'Foo  '
>>> f"{5:03d}"          # Zero-pad to 3 digits
'005'

Precision#

>>> f"{0.658712358:.3f}"           # 3 decimal places
'0.659'
>>> f"{'abracadabra':.6}"         # Truncate string to 6 characters
'abraca'
>>> f"{0.658712358:6.2f}"         # Width 6, 2 decimal places
'  0.66'

Dictionary Formatting#

>>> person = {"name": "Jane", "age": 25}
>>> f"Hello, {person['name']}! You're {person['age']} years old."
"Hello, Jane! You're 25 years old."

F-strings#

F-strings (Python 3.6+) are the most concise way to embed expressions in strings:

>>> name = "Jane"
>>> age = 25
>>> f"Hello, {name}! You're {age} years old."
"Hello, Jane! You're 25 years old."

>>> f"Hello, {name.upper()}! You're {age} years old."
"Hello, JANE! You're 25 years old."

>>> balance = 5425.9292
>>> f"Balance: ${balance:.2f}"
'Balance: $5425.93'

Wildcards with fnmatch#

The fnmatch module provides Unix shell-style wildcard matching:

Pattern	Meaning
`*`	Matches everything
`?`	Matches any single character
`[seq]`	Matches any character in seq
`[!seq]`	Matches any character NOT in seq

>>> import fnmatch
>>> fnmatch.fnmatch('Lorem ipsum', 'Lorem*')
True
>>> fnmatch.fnmatch('abracadabra12', '[a-b]??[a-b]*[1-2][!3-4]')
True