update_file.py
"""
A script that replaces an old file with a new one, only if the contents
actually changed. If not, the new file is simply deleted.
This avoids wholesale rebuilds when a code (re)generation phase does not
actually change the in-tree generated code.
"""
import os
import sys
def main(old_path, new_path):
with open(old_path, 'rb') as f:
old_contents = f.read()
with open(new_path, 'rb') as f:
new_contents = f.read()
if old_contents != new_contents:
os.replace(new_path, old_path)
else:
os.unlink(new_path)
if __name__ == '__main__':
if len(sys.argv) != 3:
print("Usage: %s <path to be updated> <path with new contents>" % (sys.argv[0],))
sys.exit(1)
main(sys.argv[1], sys.argv[2])