FTBFS: from pymongo import ... ImportError: cannot import name Connection

Imported from Debian bug http://bugs.debian.org/789980:

Source: python-mongoengine
Version: 0.6.13-2
Severity: serious
Justification: fails to build from source
User: <email address hidden>
Usertags: ftbfs

Dear Maintainer,

The package fails to build:

make[2]: Entering directory '/tmp/buildd/python-mongoengine-0.6.13/docs.debian'
sphinx-build -b html -d _build/doctrees . _build/html
Making output directory...
Running Sphinx v1.2.3

Exception occurred:
  File "/tmp/buildd/python-mongoengine-0.6.13/mongoengine/connection.py", line 2, in <module>
    from pymongo import Connection, ReplicaSetConnection, uri_parser
ImportError: cannot import name Connection
The full traceback has been saved in /tmp/sphinx-err-ty4S2z.log, if you want to report the issue to the developers.

Alternative build log:
https://reproducible.debian.net/rb-pkg/unstable/amd64/python-mongoengine.html

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 3.19.0-21-generic (SMP w/8 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)