Pretty-printing a table in Python

Often you'll have a table of data. You want to print it out as text, but aligned for readability. Here is a simple module to do that. I'll discuss the code below.

First, we have format_num. This basically just adds commas to our numbers (we want it to be pretty, right?).

import locale
locale.setlocale(locale.LC_NUMERIC, "")

def format_num(num):
"""Format a number according to given places.
Adds commas, etc. Will truncate floats into ints!"""

try:
inum = int(num)
return locale.format("%.*f", (0, inum), True)

except (ValueError, TypeError):
return str(num)

Next, get_max_width gives us the maximum width of a given column in the table. We'll use this when we decide how much to pad each column.

def get_max_width(table, index):
"""Get the maximum width of the given column index"""

return max([len(format_num(row[index])) for row in table])

Finally, the money function. Note that I pass in the output stream — this makes the function more versatile (we could print to a file, StringIO(), stdout, etc.). It also makes it easier to unit test. We could have done this behind the scenes by redirecting sys.stdout, but that would be unpythonic! <G>

def pprint_table(out, table):
"""Prints out a table of data, padded for alignment
@param out: Output stream (file-like object)
@param table: The table to print. A list of lists.
Each row must have the same number of columns. """

col_paddings = []

for i in range(len(table[0])):
col_paddings.append(get_max_width(table, i))

for row in table:
# left col
print >> out, row[0].ljust(col_paddings[0] + 1),
# rest of the cols
for i in range(1, len(row)):
col = format_num(row[i]).rjust(col_paddings[i] + 2)
print >> out, col,
print >> out

And we top it off with a bit of test code.

if __name__ == "__main__":
table = [["", "taste", "land speed", "life"],
["spam", 300101, 4, 1003],
["eggs", 105, 13, 42],
["lumberjacks", 13, 105, 10]]

import sys
out = sys.stdout
pprint_table(out, table)

The output:

                 taste   land speed    life
spam           300,101            4   1,003
eggs               105           13      42
lumberjacks         13          105      10

The linked zip file has unit tests that exercise the code a bit more thoroughly.

Vinicius Ruoso

December 14th, 2007 at 6:00 am

Hello,

I work in a Federal University, and here we implements a huge system for 1.300.000 students of public schools.

I see you module, and add it to one of my programs. But theres something that I can’t change. I want to align the text inside the table at left. Actualy its align on the right.

Can you help me on this?
Thanks a lot

Vinicius

December 14th, 2007 at 8:20 am

Sorry,

Just solve it.

Thanks a lot
Very nice module