Question

What is the most pythonic way to read in a named file, strip lines that are either empty, contain only spaces, or have # as a first character, and then process remaining lines? Assume it all fits easily in memory.

Note: it’s not tough to do this — what I’m asking is for the most pythonic way. I’ve been writing a lot of Ruby and Java and have lost my feel.

Here’s a strawman:

file_lines = [line.strip() for line in open(config_file, 'r').readlines() if len(line.strip()) > 0]
for line in file_lines:
  if line[0] == '#':
    continue
  # Do whatever with line here.

I’m interested in concision, but not at the cost of becoming hard to read.

Answer 1

lines = [r for r in open(thefile) if not r.isspace() and r[0] != '#']

The .isspace() method of strings is by far the best way to test if a string is entirely whitespace — no need for contortions such as len(r.strip()) == 0 (ech;-).