Warnings in Python 3.8

[tirkarthi]

• Deprecation warnings are raised due to invalid escape sequences. This can be fixed by using raw strings or escaping the literals. pyupgrade also helps in automatic conversion : https://github.com/asottile/pyupgrade/
• Syntax warning due to comparison of literals using is.

find . -iname '*.py' | grep -v example | xargs -P4 -I{} python3.8 -Wall -m py_compile {}
./pretrainedmodels/models/wideresnet.py:38: DeprecationWarning: invalid escape sequence \d
  blocks = [sum([re.match('group%d.block\d+.conv0.weight'%j, k) is not None
./pretrainedmodels/models/dpn.py:255: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if block_type is 'proj':
./pretrainedmodels/models/dpn.py:258: SyntaxWarning: "is" with a literal. Did you mean "=="?
  elif block_type is 'down':
./pretrainedmodels/models/dpn.py:262: SyntaxWarning: "is" with a literal. Did you mean "=="?
  assert block_type is 'normal'