NumPy: Pretty print tabular data

Question

I would like to print NumPy tabular array data, so that it looks nice. R and database consoles seem to demonstrate good abilities to do this. However, NumPy's built-in printing of tabular arrays looks like garbage:

import numpy as np
dat_dtype = {
    'names' : ('column_one', 'col_two', 'column_3'),
    'formats' : ('i', 'd', '|S12')}
dat = np.zeros(4, dat_dtype)
dat['column_one'] = range(4)
dat['col_two'] = 10**(-np.arange(4, dtype='d') - 4)
dat['column_3'] = 'ABCD'
dat['column_3'][2] = 'long string'

print(dat)
# [(0, 0.0001, 'ABCD') (1, 1.0000000000000001e-005, 'ABCD')
#  (2, 9.9999999999999995e-007, 'long string')
#  (3, 9.9999999999999995e-008, 'ABCD')]

print(repr(dat))
# array([(0, 0.0001, 'ABCD'), (1, 1.0000000000000001e-005, 'ABCD'),
#        (2, 9.9999999999999995e-007, 'long string'),
#        (3, 9.9999999999999995e-008, 'ABCD')], 
#       dtype=[('column_one', '<i4'), ('col_two', '<f8'), ('column_3', '|S12')])

I would like something that looks more like what a database spits out, for example, postgres-style:

 column_one | col_two |  column_3
------------+---------+-------------
          0 |  0.0001 | ABCD
          1 |  1e-005 | long string
          2 |  1e-008 | ABCD
          3 |  1e-007 | ABCD

Are there any good third-party Python libraries to format nice looking ASCII tables?

I'm using Python 2.5, NumPy 1.3.0.

Answer 1

I seem to be having good output with prettytable:

from prettytable import PrettyTable
x = PrettyTable(dat.dtype.names)
for row in dat:
    x.add_row(row)
# Change some column alignments; default was 'c'
x.align['column_one'] = 'r'
x.align['col_two'] = 'r'
x.align['column_3'] = 'l'

And the output is not bad. There is even a border switch, among a few other options:

>>> print(x)
+------------+---------+-------------+
| column_one | col_two |   column_3  |
+------------+---------+-------------+
|          0 |  0.0001 | ABCD        |
|          1 |  1e-005 | ABCD        |
|          2 |  1e-006 | long string |
|          3 |  1e-007 | ABCD        |
+------------+---------+-------------+
>>> print(x.get_string(border=False))
 column_one  col_two    column_3  
          0   0.0001  ABCD        
          1   1e-005  ABCD        
          2   1e-006  long string 
          3   1e-007  ABCD        

Answer 2

you can take advantage of array comprehension and use printf format strings:

for c1, c2, c3 in dat:  
    print "%2f | %8e | %s" % (c1, c2, c3)

https://en.wikipedia.org/wiki/Printf_format_string
And you can get even more customized if you go up to version 2.7

Answer 3

The tabulate package works nicely for Numpy arrays:

import numpy as np
from tabulate import tabulate

m = np.array([[1, 2, 3], [4, 5, 6]])
headers = ["col 1", "col 2", "col 3"]

# tabulate data
table = tabulate(m, headers, tablefmt="fancy_grid")

# output
print(table)

(Above code is Python 3; for Python 2 add from __future__ import print_function at top of script)

Output:

╒═════════╤═════════╤═════════╕
│   col 1 │   col 2 │   col 3 │
╞═════════╪═════════╪═════════╡
│       1 │       2 │       3 │
├─────────┼─────────┼─────────┤
│       4 │       5 │       6 │
╘═════════╧═════════╧═════════╛

The package installs via pip:

$ pip install tabulate     # (use pip3 for Python 3 on some systems)

Answer 4

You might want to check out Pandas which has a lot of nice features for dealing with tabular data and seems to lay things out better when printing (It is designed be a python replacement for R):

http://pandas.pydata.org/