ERROR: Cannot install python-doctr, python-doctr[tf-cpu]==0.5.1a0 and tensorflow-cpu==2.8.0 because these package versions have conflicting dependencies.

The conflict is caused by:
    python-doctr[tf-cpu] 0.5.1a0 depends on keras<2.7.0
    tensorflow-cpu 2.8.0 depends on keras<2.9 and >=2.8.0rc0
    python-doctr[tf-cpu] 0.5.1a0 depends on keras<2.7.0
    tensorflow-cpu 2.9.1 depends on keras<2.10.0 and >=2.9.0rc0
    python-doctr[tf-cpu] 0.5.1a0 depends on keras<2.7.0
    tensorflow-cpu 2.9.0 depends on keras<2.10.0 and >=2.9.0rc0
    python-doctr[tf-cpu] 0.5.1a0 depends on keras<2.7.0
    tensorflow-cpu 2.8.2 depends on keras<2.9 and >=2.8.0rc0
    python-doctr[tf-cpu] 0.5.1a0 depends on keras<2.7.0
    tensorflow-cpu 2.8.1 depends on keras<2.9 and >=2.8.0rc0

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts