How to ignore files that start with '.' and print the rest?

Question

Hi everyone I'm working on a school project where we are writing code to implement our own built unix shell in python. I'm stuck on this small part with the ls -a command where I want to ignore the .(dot) files. This is the code I have, I'm not sure how to finish it.

  if 'a' not in flags:
    for files in file_list:
      if files.startswith('.'):
        #ignore . files

Answer 1

A handful of options are available:

• Invert the condition:

  if 'a' not in flags:
    for files in file_list:
      if not files.startswith('.'):
        print(files)
  

• Continue the loop without printing if the file matches:

  if 'a' not in flags:
    for files in file_list:
      if files.startswith('.'):
        continue
      print(files)
  

• Combine the two conditions together to make the code less nested

  for files in file_list:
    if 'a' in flags or (not files.startswith('.')):
      print(files)
  

• Separate filtering from iteration:

  if 'a' not in flags:
    file_list = [files for files in file_list if not files.startswith('.')
  # more if-statements to process other flags of interest, 
  # e.g. if a flag for sorting is specified, sort the files
  for files in file_list:
     print(files)
  

I would lean toward the first option in the simplest case, or the last option if you need extensible logic that scales to more flags. I used a list comprehension for shorthand, but you can also call a function that handles the list, write a handwritten loop that updates the file list, or something else.

I would also add the nit that the variable which you call files refers to a single file at a time, so it should be named file (or if there's ambiguity between file names and file objects, perhaps file_name). I've left it as-is in the answer for consistency with your existing code.

Answer 2

#Creates empty list
files_no_period = [
      ]

if 'a' not in flags:
  for file in file_list:
    if not files.startswith('.'):
      files_no_period.append(file)

#Prints files in list
print ("\n".join(files_no_period))

"""
- Changed 'for files' to 'for file', just because you are going through each file on at a time.
- Changed if statement to if not, meaning if file isn't starting with a '.'.
- Add each file that doesn't start with '.' to a list.
- List all files from the list of files that don't start with a '.'.
"""