Question

Here’s a concise example:

x.py:

class x:
  var = 'from x.py'

y.py:

class x:
  var = 'from y.py'

test.py

import imp
def write_module(filename):
  fp = open('z.py', 'w')
  fp.write(open(filename).read())
  fp.close()

write_module('x.py')
import z
print(z.x.var) # Prints 'from x.py'
write_module('y.py')
imp.reload(z)
print(z.x.var) # Prints 'from x.py'

I’m not sure why both print statements are the same. How can I make python use the new definition of class x after reload()?

Answer 1

This happens because the file creation dates (of z.py and its compiled counterpart z.pyc) are identical, so Python thinks that the file is unchanged and doesn’t recompile it.

Actually, when I was trying and re-trying your code, it once worked as expected – probably because the two files happened to be created on either side of the system clock’s second-changeover.

import imp
import time
def write_module(filename):
  fp = open('z.py', 'w')
  fp.write(open(filename).read())
  fp.close()

write_module('x.py')
import z
print(z.x.var) # Prints 'from x.py'
time.sleep(1)  # Wait one second
write_module('y.py')
imp.reload(z)
print(z.x.var) # Prints 'from y.py'

shows the expected result.