podio_class_generator: only write files if their content changed

[andresailer]

Avoids spurious re-compilation
BEGINRELEASENOTES

• podio_class_generator: only write files if their content changed

ENDRELEASENOTES

[vvolkl]

Great, the recompilation issue was indeed an annoyance when using podio.

[vvolkl]

These lines could be slightly more "pythonic" with a with statement:

with open(fullname, "r+") as _f:
  existing_content = _f.read()
  if existing_content != content:
    _f.write(content)

[andresailer]

#!/usr/bin/env python
content ='foo bar'
fullname = 'temp.txt'
with open(fullname, "r+") as _f:
  existing_content = _f.read()
  if existing_content != content:
    _f.write(content)

Errors if temp.txt does not exist

$ python testRead.py
Traceback (most recent call last):
  File "testRead.py", line 6, in <module>
    with open(fullname, "r+") as _f:
IOError: [Errno 2] No such file or directory: 'temp.txt'

So we would still need one path for exists, one without.

[vvolkl]

That's true, I overlooked that in one case the file won't exist yet. Taking that in consideration I think the code is best as it is!

[andresailer]

There are many things to be cleaned up, especially in view of python3 compatibility (#66)