build hacking

installing 'python3.7-hacking-1.1.0'
these derivations will be built:
  /nix/store/l9gqh63w1z4lbbkyrra1swhamjwmywnk-python3.7-hacking-1.1.0.drv
building '/nix/store/l9gqh63w1z4lbbkyrra1swhamjwmywnk-python3.7-hacking-1.1.0.drv'...
unpacking sources
unpacking source archive /nix/store/wv08737wix6png84a7cpkc7gbi2y4rci-hacking-1.1.0.tar.gz
source root is hacking-1.1.0
setting SOURCE_DATE_EPOCH to timestamp 1525785645 of file hacking-1.1.0/setup.cfg
patching sources
configuring
building
Fatal Python error: initsite: Failed to import the site module
Traceback (most recent call last):
  File "/nix/store/f3qsw5vv81rdr3i2jyzzma35f127akgb-python2.7-setuptools-40.8.0/lib/python2.7/site-packages/site.py", line 73, in <module>
    __boot()
  File "/nix/store/f3qsw5vv81rdr3i2jyzzma35f127akgb-python2.7-setuptools-40.8.0/lib/python2.7/site-packages/site.py", line 26, in __boot
    import imp  # Avoid import loop in Python 3
  File "/nix/store/gbwx5sc4w0i0ipnmsa0nsk88svs983vl-python3-3.7.2/lib/python3.7/imp.py", line 27, in <module>
    import tokenize
  File "/nix/store/gbwx5sc4w0i0ipnmsa0nsk88svs983vl-python3-3.7.2/lib/python3.7/tokenize.py", line 33, in <module>
    import re
  File "/nix/store/gbwx5sc4w0i0ipnmsa0nsk88svs983vl-python3-3.7.2/lib/python3.7/re.py", line 143, in <module>
    class RegexFlag(enum.IntFlag):
AttributeError: module 'enum' has no attribute 'IntFlag'
builder for '/nix/store/l9gqh63w1z4lbbkyrra1swhamjwmywnk-python3.7-hacking-1.1.0.drv' failed with exit code 1
error: build of '/nix/store/l9gqh63w1z4lbbkyrra1swhamjwmywnk-python3.7-hacking-1.1.0.drv' failed
nix-env -f . -i 'python3.7-hacking'  5.02s user 0.53s system 73% cpu 7.493 total