How to install optional dependency?

[cifkao]

I wanted to add a package to my project as an optional dependency, so I ran poetry add --optional nopdb. While this did update pyproject.toml and poetry.lock, it did not seem to actually install the package:

$ poetry add --optional nopdb            
Using version ^0.2.0 for nopdb                    
                                                  
Updating dependencies                                                                                
Resolving dependencies... (39.9s)                                                                                                                                                                         
                                                  
Writing lock file               
                                                  
No dependencies to install or update

$ python                                                                                                                                      
Python 3.9.7 (default, Sep 16 2021, 13:09:58)                                                                                                                                                             
[GCC 7.5.0] :: Anaconda, Inc. on linux                                                                                                                                                                    
Type "help", "copyright", "credits" or "license" for more information.                                                                                                                                    
>>> import nopdb                                                                                                                                                                                          
Traceback (most recent call last):                                                                                                                                                                        
  File "<stdin>", line 1, in <module>                                                                                                                                                                     
ModuleNotFoundError: No module named 'nopdb' 

Without --optional, everything works:

$ poetry add nopdb
Using version ^0.2.0 for nopdb

Updating dependencies
Resolving dependencies... (40.0s)

Writing lock file

Package operations: 1 install, 0 updates, 0 removals

  • Installing nopdb (0.2.0)
$ python
Python 3.9.7 (default, Sep 16 2021, 13:09:58) 
[GCC 7.5.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import nopdb
>>>

Is this the intended behavior? If yes, how do I actually choose to install the package?

I'm using Poetry version 1.1.13.

[abn]

You will have to assign the optional dependency to an extra.

Once you have done that you can install it using the --extras flag.

poetry install --extras nopdb

[cifkao]

Thanks. I tried this, but it didn't help:

$ poetry install -E notebook
Installing dependencies from lock file
Warning: The lock file is not up to date with the latest changes in pyproject.toml. You may be getting outdated dependencies. Run update to update them.

No dependencies to install or update

Installing the current project: my-project (0.1.0)

I guess this is because I had only updated pyproject.toml (by hand) and not the lockfile.

Only after doing poetry update nopdb did this actually install the package:

$ poetry update nopdb                                                                                                                         
Updating dependencies                                                                                                                                                                                     
Resolving dependencies... (40.3s)
                                                  
Writing lock file                                                                                                                                                                                         
                                                                                                                                                                                                          
No dependencies to install or update
$ poetry install -E notebook
Installing dependencies from lock file                                                                                                                                                                    
                                                                                                                                                                                                          
Package operations: 1 install, 0 updates, 0 removals                                                                                                                                                      
                                                                                                                                                                                                          
  • Installing nopdb (0.2.0)          
                                                                                                                                                                                                          
Installing the current project: my-project (0.1.0)

So, all in all, to add an optional dependency and make sure it's installed, I had to run 3 or 4 different commands and edit a file by hand.

[abn]

Poetry not regenerating the lock file on extras change is probably a bug.

The lockfile issue was warned in the logs, so not really a bug. But should be addressed when an extra is added via cli.

As for editing the toml for extras, I concur, this requires improvements.

[cifkao]

I see. So what would be the right way to update the lockfile after editing pyproject.toml? poetry lock --no-update?

[cifkao]

Also, it would be really useful if the warning also told you which dependencies do not match, or if there was a command to check that.

[abn]

I see. So what would be the right way to update the lockfile after editing pyproject.toml? poetry lock --no-update?

This is what I would do.

Also, it would be really useful if the warning also told you which dependencies do not match, or if there was a command to check that.

That would be a more expensive operation with not much gained imho. And I suspect the output might be a bit too verbose. Right now the lockfile is identified as stale if the checksum of relevant sections in the pyproject.toml do not match what is in the lockfile.

You can however use the show command to list outdated dependencies etc.