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Merge pull request #10751 from wiggin15/main
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Fix inconsistency in dependency resolution documentation
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@pfmoore
pfmoore authored Apr 22, 2024
2 parents 58a01ff + abb109e commit 46a342b
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54 changes: 28 additions & 26 deletions docs/html/topics/dependency-resolution.md
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Expand Up @@ -175,22 +175,24 @@ When you get a `ResolutionImpossible` error, you might see something
like this:

```{pip-cli}
$ pip install "pytest < 4.6" pytest-cov==2.12.1
$ pip install package_coffee==0.44.1 package_tea==4.3.0
[regular pip output]
ERROR: Cannot install pytest-cov==2.12.1 and pytest<4.6 because these package versions have conflicting dependencies.
ERROR: Cannot install package_coffee==0.44.1 and package_tea==4.3.0 because these package versions have conflicting dependencies.
The conflict is caused by:
The user requested pytest<4.6
pytest-cov 2.12.1 depends on pytest>=4.6
package_coffee 0.44.1 depends on package_water<3.0.0,>=2.4.2
package_tea 4.3.0 depends on package_water==2.3.1
```

In this example, pip cannot install the packages requested because they are
asking for conflicting versions of pytest.
In this example, pip cannot install the packages you have requested,
because they each depend on different versions of the same package
(``package_water``):

- `pytest-cov` version `2.12.1`, requires `pytest` with a version or equal to
`4.6`.
- `package_tea` version `4.3.0` depends on version `2.3.1` of
`package_water`
- ``package_coffee`` version ``0.44.1`` depends on a version of
``package_water`` that is less than ``3.0.0`` but greater than or equal to
``2.4.2``
- ``package_tea`` version ``4.3.0`` depends on version ``2.3.1`` of
``package_water``

Sometimes these messages are straightforward to read, because they use
commonly understood comparison operators to specify the required version
Expand All @@ -199,16 +201,16 @@ commonly understood comparison operators to specify the required version
However, Python packaging also supports some more complex ways for
specifying package versions (e.g. `~=` or `*`):

| Operator | Description | Example |
| -------- | -------------------------------------------------------------- | --------------------------------------------------- |
| `>` | Any version greater than the specified version. | `>3.1`: any version greater than `3.1`. |
| `<` | Any version less than the specified version. | `<3.1`: any version less than `3.1`. |
| `<=` | Any version less than or equal to the specified version. | `<=3.1`: any version less than or equal to `3.1`. |
| `>=` | Any version greater than or equal to the specified version. | `>=3.1`: version `3.1` and greater. |
| `==` | Exactly the specified version. | `==3.1`: only `3.1`. |
| `!=` | Any version not equal to the specified version. | `!=3.1`: any version other than `3.1`. |
| `~=` | Any compatible{sup}`1` version. | `~=3.1`: any version compatible{sup}`1` with `3.1`. |
| `*` | Can be used at the end of a version number to represent _all_. | `==3.1.*`: any version that starts with `3.1`. |
| Operator | Description | Example |
| -------- | -------------------------------------------------------------- | ---------------------------------------------------- |
| `>` | Any version greater than the specified version. | `>3.1`: any version greater than `3.1`. |
| `<` | Any version less than the specified version. | `<3.1`: any version less than `3.1`. |
| `<=` | Any version less than or equal to the specified version. | `<=3.1`: any version less than or equal to `3.1`. |
| `>=` | Any version greater than or equal to the specified version. | `>=3.1`: any version greater than or equal to `3.1`. |
| `==` | Exactly the specified version. | `==3.1`: only version `3.1`. |
| `!=` | Any version not equal to the specified version. | `!=3.1`: any version other than `3.1`. |
| `~=` | Any compatible{sup}`1` version. | `~=3.1`: any version compatible{sup}`1` with `3.1`. |
| `*` | Can be used at the end of a version number to represent _all_. | `==3.1.*`: any version that starts with `3.1`. |

{sup}`1` Compatible versions are higher versions that only differ in the final segment.
`~=3.1.2` is equivalent to `>=3.1.2, ==3.1.*`. `~=3.1` is equivalent to `>=3.1, ==3.*`.
Expand Down Expand Up @@ -237,7 +239,7 @@ package version.

In our first example both `package_coffee` and `package_tea` have been
_pinned_ to use specific versions
(`package_coffee==0.44.1b0 package_tea==4.3.0`).
(`package_coffee==0.44.1 package_tea==4.3.0`).

To find a version of both `package_coffee` and `package_tea` that depend on
the same version of `package_water`, you might consider:
Expand All @@ -252,20 +254,20 @@ In the second case, pip will automatically find a version of both
`package_coffee` and `package_tea` that depend on the same version of
`package_water`, installing:

- `package_coffee 0.46.0b0`, which depends on `package_water 2.6.1`
- `package_tea 4.3.0` which _also_ depends on `package_water 2.6.1`
- `package_coffee 0.44.1`, which depends on `package_water 2.6.1`
- `package_tea 4.4.3` which _also_ depends on `package_water 2.6.1`

If you want to prioritize one package over another, you can add version
specifiers to _only_ the more important package:

```{pip-cli}
$ pip install package_coffee==0.44.1b0 package_tea
$ pip install package_coffee==0.44.1 package_tea
```

This will result in:

- `package_coffee 0.44.1b0`, which depends on `package_water 2.6.1`
- `package_tea 4.1.3` which also depends on `package_water 2.6.1`
- `package_coffee 0.44.1`, which depends on `package_water 2.6.1`
- `package_tea 4.4.3` which _also_ depends on `package_water 2.6.1`

Now that you have resolved the issue, you can repin the compatible
package versions as required.
Expand Down
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