Version Range Specifiers (>=, <, !=)

Version ranges allow you to specify flexible dependency bounds. PEP 440 defines several comparison operators that can be combined with commas to create compound specifiers.

requirements.txt with ranges:

django>=4.2,<5.0
sqlalchemy>=2.0,!=2.0.0
celery>=5.3,<6
redis>=4.5
pydantic>=2.0,<3.0

Converted to pyproject.toml:

[project]
dependencies = [
    "django>=4.2,<5.0",
    "sqlalchemy>=2.0,!=2.0.0",
    "celery>=5.3,<6",
    "redis>=4.5",
    "pydantic>=2.0,<3.0",
]

PEP 440 version specifiers reference:

Operator	Meaning	Example
==	Exact match	django==4.2.8
>=	Minimum version	flask>=3.0
<=	Maximum version	numpy<=1.26
!=	Exclude version	sqlalchemy!=2.0.0
~=	Compatible release	requests~=2.31
>	Strictly greater	click>8.0
<	Strictly less	django<5.0

Compound specifiers combine multiple operators with commas. For example, >=4.2,<5.0 means "at least 4.2 but below 5.0." This is the most common pattern for major-version pinning: accepting patches and minor releases while avoiding breaking changes in the next major version.

The != operator is useful for excluding known-buggy releases. In the example above, sqlalchemy>=2.0,!=2.0.0 skips the initial 2.0.0 release (which had known issues) while accepting all subsequent 2.x releases.