What does it mean if poetry.lock contains the same package twice?

Question

I've just discovered after a poetry update that the generated package.lock file contains the block

[[package]]
name = "black"
version = "21.8b0"
description = "The uncompromising code formatter."
category = "dev"
optional = false
python-versions = ">=3.6.2"

[package.dependencies]
click = ">=7.1.2"
mypy-extensions = ">=0.4.3"
pathspec = ">=0.9.0,<1"
platformdirs = ">=2"
regex = ">=2020.1.8"
tomli = ">=0.2.6,<2.0.0"
typing-extensions = {version = ">=3.10.0.0", markers = "python_version < \"3.10\""}

[package.extras]
colorama = ["colorama (>=0.4.3)"]
d = ["aiohttp (>=3.6.0)", "aiohttp-cors (>=0.4.0)"]
jupyter = ["ipython (>=7.8.0)", "tokenize-rt (>=3.2.0)"]
python2 = ["typed-ast (>=1.4.2)"]
uvloop = ["uvloop (>=0.15.2)"]

[[package]]
name = "black"
version = "21.9b0"
description = "The uncompromising code formatter."
category = "dev"
optional = false
python-versions = ">=3.6.2"

[package.dependencies]
click = ">=7.1.2"
mypy-extensions = ">=0.4.3"
pathspec = ">=0.9.0,<1"
platformdirs = ">=2"
regex = ">=2020.1.8"
tomli = ">=0.2.6,<2.0.0"
typing-extensions = {version = ">=3.10.0.0", markers = "python_version < \"3.10\""}

[package.extras]
colorama = ["colorama (>=0.4.3)"]
d = ["aiohttp (>=3.6.0)", "aiohttp-cors (>=0.4.0)"]
jupyter = ["ipython (>=7.8.0)", "tokenize-rt (>=3.2.0)"]
python2 = ["typed-ast (>=1.4.2)"]
uvloop = ["uvloop (>=0.15.2)"]

[[package]]
name = "black"
version = "21.10b0"
description = "The uncompromising code formatter."
category = "dev"
optional = false
python-versions = ">=3.6.2"

[package.dependencies]
click = ">=7.1.2"
mypy-extensions = ">=0.4.3"
pathspec = ">=0.9.0,<1"
platformdirs = ">=2"
regex = ">=2020.1.8"
tomli = ">=0.2.6,<2.0.0"
typing-extensions = {version = ">=3.10.0.0", markers = "python_version < \"3.10\""}

[package.extras]
colorama = ["colorama (>=0.4.3)"]
d = ["aiohttp (>=3.7.4)"]
jupyter = ["ipython (>=7.8.0)", "tokenize-rt (>=3.2.0)"]
python2 = ["typed-ast (>=1.4.3)"]
uvloop = ["uvloop (>=0.15.2)"]

As you can see, there is black 21.8b0 and black 21.9b0 and black 21.10b0. What does that mean? Which version will be installed?

Other references

• https://github.com/python-poetry/poetry-plugin-export/issues/28

Answer 1

This looks like a dump of the intermediate pool of options to be considered, called Transactions in poetry (e.g. packages with versions depending on different platform markers). The decision could be by the "latest" rule, by default.

I can reproduce this behaviour with

[tool.poetry.dependencies]
python = "~3.8"
numpy = [
    {version="1.18.*",markers="python_version=='3.8.*'"},
    {version="1.21.*",markers="python_version=='3.9.*'"},
]

and poetry install --dry-run -vv produces both versions in the lock file.

Which poetry you use? I think the file got cleaned in recent releases and indicates the final choice only.