Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

`poetry update` AttributeError: 'EmptyConstraint' object has no attribute 'allows'

See original GitHub issue

I am on the latest Poetry version.
I have searched the issues of this repo and believe that this is not a duplicate.
If an exception occurs when executing a command, I executed it again in debug mode (-vvv option). Gist of output is: https://gist.github.com/mdengler/7be12f9c481567c7872bc2ea712464b6

OS version and name: Fedora 34

$ cat /etc/fedora-release 
Fedora release 34 (Thirty Four)

Poetry version: Poetry version 1.1.6

$ poetry --version
Poetry version 1.1.6

Link of a Gist with the contents of your pyproject.toml file: Unpublished software, so if there is a need for this file, I can provide privately.

Issue

I have received this error message:

$ poetry update 
Updating dependencies                                                                                                                                         
Resolving dependencies... (34.4s)                                                                                                                             
                                                                                                                                                              
Writing lock file                                                                                                                                             
                                                                                                                                                              
  AttributeError                                                                                                                                              
                                                                                                                                                              
  'EmptyConstraint' object has no attribute 'allows'                                                                                                          
                                                                                                                                                              
  at ~/.local/lib/python3.9/site-packages/poetry/core/version/markers.py:291 in validate                                                                      
      287│                                                                                                                                                    
      288│         if self._name not in environment:                                                                                                          
      289│             return True                                                                                                                            
      290│                                                                                                                                                    
    → 291│         return self._constraint.allows(self._parser(environment[self._name]))                                                                      
      292│                                                                                                                                                    
      293│     def without_extras(self):  # type: () -> MarkerTypes                                                                                           
      294│         return self.exclude("extra")                                                                                                               
      295│

I made this change as a workaround:

$ diff -uw ~/.local/lib/python3.9/site-packages/poetry/core/version/markers.py{~,}
--- /home/martin/.local/lib/python3.9/site-packages/poetry/core/version/markers.py~     2021-04-21 11:44:56.085692322 -0400
+++ /home/martin/.local/lib/python3.9/site-packages/poetry/core/version/markers.py      2021-08-19 11:38:17.934769254 -0400
@@ -288,6 +288,9 @@
         if self._name not in environment:
             return True
 
+        if not hasattr(self._constraint, "allows"):
+            return True
+
         return self._constraint.allows(self._parser(environment[self._name]))
 
     def without_extras(self):  # type: () -> MarkerTypes
$ diff -uw ~/.local/lib/python3.9/site-packages/poetry/core/version/markers.py{~,}
--- /home/martin/.local/lib/python3.9/site-packages/poetry/core/version/markers.py~     2021-04-21 11:44:56.085692322 -0400
+++ /home/martin/.local/lib/python3.9/site-packages/poetry/core/version/markers.py      2021-08-19 11:38:17.934769254 -0400
@@ -288,6 +288,9 @@
         if self._name not in environment:
             return True
 
+        if not hasattr(self._constraint, "allows"):
+            return True
+
         return self._constraint.allows(self._parser(environment[self._name]))
 
     def without_extras(self):  # type: () -> MarkerTypes

I gathered some extra debugging information that points to greenlet and sqlalchemy as being involved in the issue: https://gist.github.com/mdengler/7be12f9c481567c7872bc2ea712464b6