Re-implement `column -t filename` using python and centering the columns.

column.py

#!/usr/bin/env python3

import sys
import itertools

def three_passes_and_storage():
    # Read file and split each line into fields (by whitespace)
    with open(sys.argv[1]) as f:
        lines = [line.split() for line in f.readlines()]
    # Check that each line has the same number of fields
    num_fields = len(lines[0])
    for n, line in enumerate(lines):
        if len(line) != num_fields:
            print('Line {} has wrong number of columns: expected {}, got {}'.format(n, num_fields, len(line)))
            sys.exit(1)
    # Calculate the maximum length of each field
    max_column_widths = [0] * num_fields
    for line in lines:
        line_widths = (len(field) for field in line)
        max_column_widths = [max(z) for z in zip(max_column_widths, line_widths)]
    # Now print them centered using the max_column_widths
    spacing = 4
    format_spec = (' ' * spacing).join('{:^' + str(n) + '}' for n in max_column_widths)
    for line in lines:
        print(format_spec.format(*line))


def two_passes():
    # Read file and split each line into fields (by whitespace)
    with open(sys.argv[1]) as f:
        line = f.readline().split()
        num_fields = len(line)
        max_column_widths = (len(field) for field in line)
        for n, line in enumerate(f, start=1):
            line = line.split()
            if len(line) != num_fields:
                print('Line {} has wrong number of columns: expected {}, got {}'.format(n, num_fields, len(line)))
                sys.exit(1)
            line_widths = (len(field) for field in line)
            max_column_widths = [max(z) for z in zip(max_column_widths, line_widths)]

    # Now print them centered using the max_column_widths
    spacing = 4
    format_spec = (' ' * spacing).join('{:^' + str(n) + '}' for n in max_column_widths)
    with open(sys.argv[1]) as f:
        for line in f:
            print(format_spec.format(*line.split()))

def two_passes_and_storage():
    # Read file and split each line into fields (by whitespace)
    with open(sys.argv[1]) as f:
        line = f.readline().split()
        num_fields = len(line)
        max_column_widths = (len(field) for field in line)
        lines = [line]
        for n, line in enumerate(f, start=1):
            line = line.split()
            lines.append(line)
            if len(line) != num_fields:
                print('Line {} has wrong number of columns: expected {}, got {}'.format(n, num_fields, len(line)))
                sys.exit(1)
            line_widths = (len(field) for field in line)
            max_column_widths = [max(z) for z in zip(max_column_widths, line_widths)]

    # Now print them centered using the max_column_widths
    spacing = 4
    format_spec = (' ' * spacing).join('{:^' + str(n) + '}' for n in max_column_widths)
    for line in lines:
            print(format_spec.format(*line))

three_passes_and_storage()
print('=' * 40)
two_passes()
print('=' * 40)
two_passes_and_storage()