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Basic Python Syntax and Object Model

Python source is organized into expressions that produce values and statements that control binding, execution, and definitions. Indentation delimits suites after headers ending in :.

temperature_c = 21.5
if temperature_c < 0:
    state = "frozen"
else:
    state = "liquid"

Names bind objects​

Assignment binds a name; it does not declare a storage box or copy the value:

first = [1, 2]
second = first
second.append(3)
assert first == [1, 2, 3]

Use .copy(), slicing, or a deeper-copy strategy when independent mutable state is required. Whether an operation mutates depends on the object's type and API.

Built-in value families​

  • numeric: int, float, complex, bool;
  • text and binary: str, bytes, bytearray;
  • sequences: list, tuple, range;
  • mappings and sets: dict, set, frozenset;
  • absence sentinel: None.

These categories imply different protocols. For example, a string is immutable, a list is mutable, and dictionary keys must be hashable.

Operators and comparison​

/ performs true division; // performs floor division; % gives the matching remainder. Use == for value equality and is for identity, normally with singletons such as None:

if result is None:
    handle_missing_result()

Conversion is a boundary​

Constructors such as int(text), float(text), and str(value) request a conversion and may raise an exception. Do not assume user or file input has the desired form:

try:
    quantity = int(raw_quantity)
except ValueError as error:
    raise ValueError("quantity must be an integer") from error

Namespaces and imports​

Imports bind module objects or selected names in the current namespace:

from pathlib import Path

config_path = Path("config.json")

Prefer explicit imports and avoid wildcard imports; ownership and name origin should remain visible.

Sources​