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At a glance: what each operator commits you to
| Specifier | What it allows | What it does not set |
|---|---|---|
==3.1 |
A strict match for 3.1, including zero-padded equivalent 3.1.0. | It does not match 3.1.1 or other versions merely because they start with 3.1. |
>=3.1 |
3.1 and later versions under Python’s version ordering. | No upper limit. |
~=3.1 |
3.1 or later within the 3.x release prefix; it is approximately >=3.1, ==3.*. |
It excludes 4.0 and later. |
~=3.1.2 |
3.1.2 or later within the 3.1.x release prefix; approximately >=3.1.2, ==3.1.*. |
It excludes 3.2.0 and later. |
These are specifier boundaries, not a promise that every qualifying release will be selected: pre-release handling is a separate consideration.
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What does == mean in a requirement?
Without a wildcard, ==V means a strict version match. Release segments are zero-padded for comparison, so ==1.1 matches 1.1.0. It does not match 1.1.1, 1.1a1, 1.1.dev1, or 1.1.post1.
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To match a release prefix instead, use a trailing wildcard: ==1.1.* can match versions beginning with the 1.1 release prefix. This is different from an exact pin: maintenance releases such as 1.1.1 can fall within the prefix match.
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The PyPA specification strongly discourages using == without a wildcard in dependencies for published distributions because strict pins complicate deployment of security fixes. Exact pins can still serve repeatable application deployments, particularly when the deployment uses a shared package index; that use case is different from restricting dependencies published for others to install. Read the PyPA version specifiers specification.
What does >= allow?
>=V sets an inclusive floor: versions equal to or later than V under standard Python version ordering can satisfy it. On its own, it places no ceiling on future versions. A declaration such as >=1.4,<2 adds a separate upper constraint; because the clauses are comma-separated, a candidate must satisfy both.
What does ~= mean in Python requirements?
The compatible-release operator combines a lower bound with a release-prefix limit. The number of release components determines how narrow that prefix is: additional components tighten the permitted series.
~=3.1: allow the 3.x series from 3.1
This is approximately equivalent to >=3.1, ==3.*. It allows later 3.x releases, including 3.2, but not 4.0 or later.
~=3.1.2: allow the 3.1.x series from 3.1.2
This is approximately equivalent to >=3.1.2, ==3.1.*. It allows later releases with the 3.1 prefix but not 3.2.0 or later.
~=3.1.0: the extra zero narrows the prefix
Here the prefix is 3.1.*, so it has the same broad boundary as ~=3.1.2, with a different lower bound: it starts at 3.1.0. A single-segment version such as ~=1 is not valid with this operator.
How pre-releases and exclusive bounds affect the result
A written range should not be read as an unconditional list of every version that sorts between its bounds. Pre-releases, including development releases, are implicitly excluded unless they are already installed, explicitly requested, or the only available version satisfying the requirements. Dependency resolution tools are expected to follow this default while allowing users to request other behavior.
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How to choose a specifier
- Use
==Vwhen the requirement genuinely needs one strict version match; do not mistake it for a maintenance-series range. - Use
>=Vwhen you need to state a minimum and intend to leave later versions open, or pair it with another clause when an upper boundary is needed. - Use
~=V.Nwhen later releases within a chosen prefix are acceptable; add release components to narrow the prefix deliberately. - Check comma-separated clauses together: each one must match, and resolver pre-release behavior can further affect selection.
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