Python

Python syntax, built-in functions, and common patterns

📦 Data Types

Command	Description
`int`	Integer numbers: 42, -17, 0
`float`	Decimal numbers: 3.14, -0.5
`str`	Text strings: "hello", 'world'
`bool`	Boolean: True, False
`list`	Ordered mutable sequence: [1, 2, 3]
`tuple`	Ordered immutable sequence: (1, 2, 3)
`dict`	Key-value pairs: {"a": 1, "b": 2}
`set`	Unique unordered items: {1, 2, 3}
`None`	Null/empty value

📝 String Methods

Command	Description
`s.upper()`	Convert to uppercase
`s.lower()`	Convert to lowercase
`s.strip()`	Remove leading/trailing whitespace
`s.split(sep)`	Split string into list
`s.join(list)`	Join list into string
`s.replace(old, new)`	Replace substring
`s.find(sub)`	Find substring index (-1 if not found)
`s.startswith(pre)`	Check if starts with prefix
`s.endswith(suf)`	Check if ends with suffix
`f"Hello {name}"`	F-string formatting

📋 List Methods

Command	Description
`list.append(x)`	Add item to end
`list.extend(iter)`	Add all items from iterable
`list.insert(i, x)`	Insert item at index
`list.remove(x)`	Remove first occurrence of x
`list.pop(i)`	Remove and return item at index
`list.sort()`	Sort list in place
`list.reverse()`	Reverse list in place
`list.index(x)`	Find index of first occurrence
`list.count(x)`	Count occurrences of x
`list[start:end:step]`	Slice list

🔑 Dictionary Methods

Command	Description
`d.keys()`	Get all keys
`d.values()`	Get all values
`d.items()`	Get all key-value pairs
`d.get(key, default)`	Get value with default
`d.pop(key)`	Remove and return value
`d.update(dict2)`	Merge another dictionary
`d.setdefault(key, val)`	Set if key missing
`key in d`	Check if key exists

🔀 Control Flow

Command	Description
`if / elif / else`	Conditional branching
`for x in iterable:`	Iterate over sequence
`while condition:`	Loop while condition true
`break`	Exit loop immediately
`continue`	Skip to next iteration
`pass`	Do nothing (placeholder)
`match value: case x:`	Pattern matching (3.10+)

⚙️ Functions

Command	Description
`def func(args):`	Define function
`return value`	Return value from function
`lambda x: x * 2`	Anonymous function
`*args`	Variable positional arguments
`**kwargs`	Variable keyword arguments
`@decorator`	Function decorator
`def func() -> int:`	Type hint for return

🛠️ Built-in Functions

Command	Description
`len(x)`	Get length of sequence
`range(start, stop, step)`	Generate number sequence
`enumerate(iter)`	Get index and value pairs
`zip(iter1, iter2)`	Pair items from iterables
`map(func, iter)`	Apply function to all items
`filter(func, iter)`	Filter items by function
`sorted(iter)`	Return sorted list
`reversed(iter)`	Return reversed iterator
`sum(iter)`	Sum all numbers
`min(iter) / max(iter)`	Get minimum/maximum
`any(iter) / all(iter)`	Check if any/all true
`isinstance(obj, type)`	Check object type
`type(obj)`	Get object type
`print()`	Output to console
`input()`	Read user input
`open(file, mode)`	Open file for reading/writing

✨ Comprehensions

Command	Description
`[x for x in iter]`	List comprehension
`[x for x in iter if cond]`	List with condition
`{x for x in iter}`	Set comprehension
`{k: v for k, v in iter}`	Dict comprehension
`(x for x in iter)`	Generator expression

📁 File I/O

Command	Description
`open(f, "r")`	Open for reading
`open(f, "w")`	Open for writing (overwrite)
`open(f, "a")`	Open for appending
`with open(f) as file:`	Context manager (auto-close)
`file.read()`	Read entire file
`file.readline()`	Read one line
`file.readlines()`	Read all lines as list
`file.write(s)`	Write string to file

⚠️ Exception Handling

Command	Description
`try: / except:`	Catch exceptions
`except Error as e:`	Catch specific exception
`finally:`	Always execute (cleanup)
`raise Exception(msg)`	Raise exception
`assert condition`	Assert condition is true

📝 Common Patterns

 # List comprehension with condition
evens = [x for x in range(10) if x % 2 == 0]

# Dictionary from two lists
d = dict(zip(keys, values))

# Read file lines
with open("file.txt") as f:
    lines = f.readlines()

# Lambda with map
doubled = list(map(lambda x: x * 2, numbers))

# Ternary expression
result = "yes" if condition else "no"

# Unpack values
a, b, *rest = [1, 2, 3, 4, 5]

# Walrus operator (3.8+)
if (n := len(data)) > 10:
    print(f"Got {n} items") 