Dependency Trees in Python

One of the nice features when working with npm for io.js/node.js is the npm list command. It provides you a simple tree view of all the dependencies your package has and their dependencies and so on.

$ npm list
packagename@0.1.0 /Users/zerok/code/packagename
├── async@0.9.0
├─┬ chai@2.1.2
│ ├── assertion-error@1.0.0
│ └─┬ deep-eql@0.1.3
│   └── type-detect@0.1.1
├─┬ chalk@1.0.0
│ ├── ansi-styles@2.0.1
│ ├── escape-string-regexp@1.0.3
│ ├─┬ has-ansi@1.0.3
│ │ ├── ansi-regex@1.1.1
│ │ └── get-stdin@4.0.1
│ ├─┬ strip-ansi@2.0.1
│ │ └── ansi-regex@1.1.1
│ └── supports-color@1.3.0
├── es6-collections@0.5.1
├── es6-promise@2.0.1

This is very useful to find out after the fact what packages were installed and what dependencies your project really has. If for nothing else this might help with learning about low-level libraries you might want to use yourself in the future…

Sadly, pip doesn’t have something like that out of the box. But here something like that would be especially useful simply because pip/setuptools/Python right now doesn’t support actual hierarchical dependency installations (similar to npm) nor an obvious dependency resolution method. Running pip freeze will only show you the final package list as installed after all the fun happened.

With “the fun” I mean that right now there is only one “final” level of dependencies in each project as all are installed into one folder and can be accessed directly. What about situations where you use library “a” that depends on “a.a” at version 1 while you also depend on “b” that requires version 2 of “a.a”? issue988 has some nice details on situations like this. Basically top-level dependencies are the most important ones and everything else is resolved more or less in a breadth-first-way.

Luckily, there is already something similar to npm list out there called pipdeptree which helps with finding possible dependency conflicts and displaying an actual dependency hierarchy.

This would be its output for one of my smaller Django projects:

$ pipdeptree
Warning!!! Possible confusing dependencies found:
* django-cms==3.0.12 -> django-classy-tags [required: >=0.5, installed: 0.5.2]
  django-sekizai==0.8.1 -> django-classy-tags [required: >=0.3.1, installed: 0.5.2]
* django-debug-toolbar==1.2.2 -> Django [required: >=1.4.2, installed: 1.7.7]
  django-cms==3.0.12 -> Django [required: >=1.4, installed: 1.7.7]
  django-mptt==0.6.1 -> Django [required: >=1.4.2, installed: 1.7.7]
  django-filer==0.9.9a1.dev1 -> Django [required: >=1.4, installed: 1.7.7]
  easy-thumbnails==2.2 -> Django [required: >=1.4.2, installed: 1.7.7]
  django-classy-tags==0.5.2 -> Django [required: >1.2, installed: 1.7.7]
  cmsplugin-filer==0.10.1 -> Django [required: >=1.4, installed: 1.7.7]
* django-cms==3.0.12 -> django-sekizai [required: >=0.7, installed: 0.8.1]
  cmsplugin-filer==0.10.1 -> django-sekizai [required: >=0.4.2, installed: 0.8.1]
  - Django [required: >=1.4, installed: 1.7.7]
  - django-cms [required: >=3.0, installed: 3.0.12]
    - Django [required: >=1.4, installed: 1.7.7]
    - South [required: >=0.7.2, installed: 1.0.2]
  - django-sekizai [required: >=0.4.2, installed: 0.8.1]
    - django-classy-tags [required: >=0.3.1, installed: 0.5.2]
      - Django [required: >1.2, installed: 1.7.7]
  - easy-thumbnails [required: >=1.0, installed: 2.2]
    - Django [required: >=1.4.2, installed: 1.7.7]
    - Pillow [installed: 2.7.0]

As you can see, pipdeptree warns you when you have multiple dependencies where the versions don’t exactly match. At this point it shows too many warnings for my taste as there are actually no conflicts up there. That being said, it’s a first step.

If you want to learn more about this whole issue, I’d recommend taking a look at issue988 as well as this great post by Vincent Driessen about his and Bruno Renié’s work on pip-tools.

Part of this effort is the pip-compile command which will hopefully soon help resolve versioning conflicts right during creation of the requirements.txt. Can’t wait for more tools on that front!

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