There is a more fundamental difference, which is what happens in a single project with a diamond-shape dependency with version mismatches, like this: A ->

There is a more fundamental difference, which is what happens in a single project with a diamond-shape dependency with version mismatches, like this: A -> B, C B -> D == 0.1 C -> D == 0.2 This dependency graph is handled easily by npm and other tools (at the expense of disk space, memory usage, etc.) and potentially small incompatibilities/gotchas, but is completely impossible to satisfy with pip.