Initialise Containers With Literals

ID

python.init_dicts_with_literals

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Efficiency

Language

Python

Tags

code-style, efficiency

Description

Reports calls to the empty constructors dict(), list(), tuple(), str(). The literal forms ({}, [], (), "") are shorter, slightly faster (no global name lookup), and clearer.

cache = dict()         # FLAW — use {}
items = list()         # FLAW — use []
empty = str()          # FLAW — use ""

cache = {}             # OK
items = []             # OK
empty_set = set()      # OK — no empty-set literal

Rationale

The empty constructor calls perform a name lookup, allocate, and return — every iteration of the program. The literal forms are produced by the bytecode compiler as a single opcode. The savings are tiny per call but consistent, and the literal form is the canonical Python style.

set() is exempt because {} is a dict literal in Python — there is no empty-set literal.

Remediation

Replace the constructor with the literal:

cache = {}
items = []
empty = ""
unit = ()

Constructors with arguments (dict(a=1), list(some_iter)) are out of scope.

References