How is "egg=" used in "pip install -e"?

Trying to test editable installs out and I'm not sure how to interpret the results.

I intentionally made a typo in the egg= portion but it was still able to locate the egg without any help from me:

root@6be8ee41b6c9:/# pip3 install -e git+https://gitlab.com/jame/clientapp.git      
Could not detect requirement name for 'git+https://gitlab.com/jame/clientapp.git', please specify one with #egg=your_package_name

root@6be8ee41b6c9:/# pip3 install -e git+https://gitlab.com/jame/clientapp.git#egg=
Could not detect requirement name for 'git+https://gitlab.com/jame/clientapp.git#egg=', please specify one with #egg=your_package_name

root@6be8ee41b6c9:/# pip3 install -e git+https://gitlab.com/jame/clientapp.git#egg=e
Obtaining e from git+https://gitlab.com/jame/clientapp.git#egg=e
  Cloning https://gitlab.com/jame/clientapp.git to /src/e
  Running setup.py (path:/src/e/setup.py) egg_info for package e produced metadata for project name clientapp. Fix your #egg=e fragments.
Installing collected packages: clientapp
  Found existing installation: ClientApp 0.7
    Can't uninstall 'ClientApp'. No files were found to uninstall.
  Running setup.py develop for clientapp
Successfully installed clientapp

root@6be8ee41b6c9:/# pip3 freeze
asn1crypto==0.24.0
-e git+https://gitlab.com/jame/clientapp.git@5158712c426ce74613215e61cab8c21c7064105c#egg=ClientApp
cryptography==2.6.1
entrypoints==0.3
keyring==17.1.1
keyrings.alt==3.1.1
pycrypto==2.6.1
PyGObject==3.30.4
pyxdg==0.25
SecretStorage==2.3.1
six==1.12.0

So if I could mess the egg name up so bad, why is it considered an error to either leave it blank or set to something empty

Solution

This is outdated notation. Nowadays one should use the following notation whenever possible:

python -m pip install 'ProjectName @ git+https://example.local/repository.git@1.3.1'

My guess, the name matters if the project is a dependency of another project. For example in a case where one wants to install A from PyPI and Z from git, but Z is a dependency of A.

python -m pip install 'A' 'git+https://example.local/repository.git#egg=Z'

or with new notation:

python -m pip install 'A' 'Z @ git+https://example.local/repository.git