Any check to see if the code written is in python 2.7 or 3 and above?

Question

I have a buggy long python project that I am trying to debug. Its messy and undocumented. I am familiar with python2.7. There are no binaries in this project. The straight forward idea is to try execute it as python2.7 file.py or python3 file.py and see which works. But as I said it is already buggy at a lot of places. So none of them is working. Is there any check or method or editor that could tell me if the code was written in python2.7 or python3?

Answer 1

Attempt to compile it. If the script uses syntax specific to a version then the compilation will fail.

$ python2 -m py_compile foo.py
$ python3 -m py_compile foo.py

Answer 2

The following statements indicate Python 2.x:

import exceptions

for i in xrange(n):
  ...

print 'No parentheses'

# raw_input doesn't exist in Python 3
response = raw_input()

try:
   ...
except ValueError, e:
   # note the comma above
   ...

These suggest Python 2, but may occur as old habits in Python 3 code:

'%d %f' % (a, b)

# integer divisions
r = float(i)/n # where i and n are integer
r = n / 2.0

These are very likely Python 3:

# f-strings
s = f'{x:.3f} {foo}'

# range returns an iterator
foo = list(range(n))

try:
   ...
except ValueError as e:
   # note the 'as' above
   ...