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Pretty-print tabular data

Project description

Pretty-print tabular data in Python.

The main use cases of the library are:

  • printing small tables without hassle: just one function call, formatting is guided by the data itself
  • authoring tabular data for lightweight plain-text markup: multiple output formats suitable for further editing or transformation
  • readable presentation of mixed textual and numeric data: smart column alignment, configurable number formatting, alignment by a decimal point

Installation

pip install tabulate

Usage

The module provides just one function, tabulate, which takes a list of lists or a similarly shaped data structure, and outputs a nicely formatted plain-text table:

>>> from __future__ import print_function
>>> from tabulate import tabulate

>>> table = [["Sun",696000,1989100000],["Earth",6371,5973.6],
...          ["Moon",1737,73.5],["Mars",3390,641.85]]
>>> print(tabulate(table))
-----  ------  -------------
Sun    696000     1.9891e+09
Earth    6371  5973.6
Moon     1737    73.5
Mars     3390   641.85
-----  ------  -------------

tabulate can pretty-print two-dimensional NumPy arrays too.

Headers

If function tabulate receives two arguments, it considers the second argument to be a list of column headers. The list of headers may be passed also out-of-order with a named argument headers=...:

>>> print(tabulate(table, headers=["Planet","R (km)", "mass (x 10^29 kg)"]))
Planet      R (km)    mass (x 10^29 kg)
--------  --------  -------------------
Sun         696000           1.9891e+09
Earth         6371        5973.6
Moon          1737          73.5
Mars          3390         641.85

Table format

There is more than one way to format a table in plain text. The output format of tabulate is defined by an optional named argument tablefmt.

Supported table formats are:

  • “plain”
  • “simple”
  • “grid”
  • “pipe”
  • “orgtbl”

plain tables do not use any pseudo-graphics to draw lines:

>>> table = [["spam",42],["eggs",451],["bacon",0]]
>>> headers = ["item", "qty"]
>>> print(tabulate(table, headers, tablefmt="plain"))
item      qty
spam       42
eggs      451
bacon       0

simple is the default format (the default may change in future versions). It corresponds to simple_tables in Pandoc Markdown extensions:

>>> print(tabulate(table, headers, tablefmt="simple"))
item      qty
------  -----
spam       42
eggs      451
bacon       0

grid is like tables formatted by Emacs’ table.el package. It corresponds to grid_tables in Pandoc Markdown extensions:

>>> print(tabulate(table, headers, tablefmt="grid"))
+--------+-------+
| item   |   qty |
+========+=======+
| spam   |    42 |
+--------+-------+
| eggs   |   451 |
+--------+-------+
| bacon  |     0 |
+--------+-------+

pipe follows the conventions of PHP Markdown Extra extension. It corresponds to pipe_tables in Pandoc. This format uses colons to indicate column alignment:

>>> print(tabulate(table, headers, tablefmt="pipe"))
| item   |   qty |
|:-------|------:|
| spam   |    42 |
| eggs   |   451 |
| bacon  |     0 |

orgtbl follows the conventions of Emacs org-mode, and is editable also in the minor orgtbl-mode. Hence its name:

>>> print(tabulate(table, headers, tablefmt="orgtbl"))
| item   |   qty |
|--------+-------|
| spam   |    42 |
| eggs   |   451 |
| bacon  |     0 |

Column alignment

tabulate is smart about column alignment. It detects columns which contain only numbers, and aligns them by a decimal point (or flushes them to the right if they appear to be integers). Text columns are flushed to the left.

You can override the default alignment with numalign and stralign named arguments. Possible column alignments are: right, center, left, decimal (only for numbers).

Aligning by a decimal point works best when you need to compare numbers at a glance:

>>> print(tabulate([[1.2345],[123.45],[12.345],[12345],[1234.5]]))
----------
    1.2345
  123.45
   12.345
12345
 1234.5
----------

Compare this with a more common right alignment:

>>> print(tabulate([[1.2345],[123.45],[12.345],[12345],[1234.5]], numalign="right"))
------
1.2345
123.45
12.345
 12345
1234.5
------

For tabulate, anything which can be parsed as a number is a number. Even numbers represented as strings are aligned properly. This feature comes in handy when reading a mixed table of text and numbers from a file:

>>> import csv ; from StringIO import StringIO
>>> table = list(csv.reader(StringIO("spam, 42\neggs, 451\n")))
>>> table
[['spam', ' 42'], ['eggs', ' 451']]
>>> print(tabulate(table))
----  ----
spam    42
eggs   451
----  ----

Number formatting

tabulate allows to define custom number formatting applied to all columns of decimal numbers. Use floatfmt named argument:

>>> print tabulate([["pi",3.141593],["e",2.718282]], floatfmt=".4f")
--  ------
pi  3.1416
e   2.7183
--  ------

Performance considerations

Such features as decimal point alignment and trying to parse everything as a number imply that tabulate:

  • needs to keep the entire table in-memory
  • has to “transpose” the table twice
  • does much more work than it may appear

It may not be suitable to pretty-print really big tables (but who’s going to do that, anyway?) or printing tables in performance sensitive applications. tabulate is about two orders of magnitude slower than simply joining lists of values with a tab, coma or other separator.

A micro-benchmark in ipython to compare tabulate with CSV file generation, and simple formatting and joining cell values with a tab:

>>> # a test table with mixed textual and numeric data
>>> table = [["some text"]+range(i,i+9) for i in range(10)]

>>> # conversion to CSV
>>> import csv ; from StringIO import StringIO
>>> csv.writer(StringIO()).writerows(table)

>>> # joining with tabs
>>> def tabulate_fast(rows):
...     return "\n".join(("\t".join(map(str,row)) for row in rows))
...

The results:

method               time (us)    rel. time
-----------------  -----------  -----------
csv to StringIO          30.80         1.33
joining with tabs        23.10         1.00
tabulate                853.00        36.93

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