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Lightweight formatting (pretty-printing) of tables and times in Python

Project description

frmt is a pretty-printing library for tables and times. The core philosophy is that it should work with minimal hassle, yet offer flexibility through elegant, lightweight design (less than 150 lines of code excluding comments).

The library consist of the following functions:

format_table() print_table() Format a list of lists as a table.
format_time_large() print_time_large() Format seconds to dd:hh:mm:ss.
format_time_small() print_time_small() Format seconds using SI-prefix and 3 significant figures, e.g. 3.45ms.
format_time() print_time() Same as *_time_small() for less than 60 seconds, same as *_time_large() otherwise.
format_fit() print_fit() Fit and align text within a width.

The format_*() functions returns a formatted string, whereas the print_*() functions are simple wrappers around the format_*() functions that prints the return string.


Install from PyPI using pip (preferred method):

pip install frmt

Or download the GitHub repository and run:

python install




The *_table() functions formats a table represented as a list of lists. Consider this example using a table of grades from 1.0 (best) to 6.0 (worst):

>>> from frmt import print_table
>>> grades = [[''      , 'Math', 'English', 'History', 'Comment'          ],
...           ['Bob'   , 1.2   , 2.1      , 5.9      , 'Failed at history'],
...           ['Jane'  , 2.4   , 1.1      , 1.4      , 'Quite good'       ],
...           ['Trevor', 2.2   , 4.4      , 3.2      , 'Somewhat average' ]]

>>> print_table(grades)
        Math  English  History  Comment
Bob     1.2   2.1      5.9      Failed at history
Jane    2.4   1.1      1.4      Quite good
Trevor  2.2   4.4      3.2      Somewhat average

The functions also work with other kinds of iterables of iterables, for instance NumPy arrays. It also supports custom alignment and formatting for each individual cell.


The align parameter can be used to change cell alignment:

  • '<' - Left aligned (default)
  • '^' - Centered
  • '>' - Right aligned

It is also possible to have different alignments for different columns by having one character for each column. For instance, to have the first column left aligned and the subsequent four right aligned, set align to '<>>>>' or, equivalently, to '<>':

>>> print_table(grades, '<>')
        Math  English  History            Comment
Bob      1.2      2.1      5.9  Failed at history
Jane     2.4      1.1      1.4         Quite good
Trevor   2.2      4.4      3.2   Somewhat average

Note that if only some columns are specified, the last specified alignment is repeated. This is useful typically when the left column is text and the remaining columns are numbers (although here it would be better to left align the rightmost column). This pattern of “repeating the last” is a core philosophy used throughout frmt to achieve flexibility.

It is also possible to have different alignments for different rows by having a list of alignment strings for each row. Again, if not all rows are specified, the last alignment string in the list is repeated for subsequent rows. For instance:

>>> print_table(grades, ['^','<^^^<'])
        Math  English  History       Comment
Bob     1.2     2.1      5.9    Failed at history
Jane    2.4     1.1      1.4    Quite good
Trevor  2.2     4.4      3.2    Somewhat average

On the header row all cells are centered ('^'). On the subsequent rows the leftmost column is left aligned, the three next ones are centered, and the last is also left aligned ('<^^^<').

Cell formatting

The format parameter can be used to format the cell contents. By default the format string '{:.3g}' is used to format numbers. This is a reasonable default, but often one would like to tune the formatting. For instance if we do not wish to display decimals in the above grading example, it can be easily achieved:

>>> print_table(grades, format='{:.0f}')
        Math  English  History  Comment
Bob     1     2        6        Failed at history
Jane    2     1        1        Quite good
Trevor  2     4        3        Somewhat average

format also accepts a function as an input to allow for greater flexibility. As an example, consider formatting the grades as letters:

>>> def letter_grade(x):
...     return 'ABCDEF'[int(round(x))-1]

>>> print_table(grades, format=letter_grade)
        Math  English  History  Comment
Bob     A     B        F        Failed at history
Jane    B     A        A        Quite good
Trevor  B     D        C        Somewhat average

The function letter_grade() throws a TypeError when applied to for instance “Bob”, so print_table() will not use it for “Bob”. Likewise for format strings; when using them on some cell content would result in an exception, print_table() resorts to using str() on it.

Following a pattern similar to align, different format strings/functions can be applied to different columns by putting them in a list. The last specified format string/function will be repeated for all subsequent columns. One can also specify different format strings/functions for different rows. In that case the lists are nested; a list with one list for each row. For example, to uppercase the header row:

>>> def str_upper(s):
...     return s.upper()

>>> print_table(grades, format=[[str_upper],[letter_grade]])
Bob     A     B        F        Failed at history
Jane    B     A        A        Quite good
Trevor  B     D        C        Somewhat average

Using the format option is not the only, and not always the best way to format the cell contents. Sometimes it may be just as good to format the cell contents before passing it to *_table(), like in this example:

>>> measurements = \
... [[0.0, 0.16159999923218293, 0.05832942704771176],
...  [0.001, 0.5415871693699631, 0.1038533048639953],
...  [0.002, 1.0020586304683154, 0.06263011126285473],
...  [0.003, 1.6493888138044273, 0.1633588946456795],
...  [0.004, 2.158470579371153, 0.16602352409683588],
...  [0.005, 2.543489191597334, 0.18539040280004443],
...  [0.006, 3.1235687589204497, 0.24946423631204423],
...  [0.007, 3.6155358393212573, 0.19856685230794482],
...  [0.008, 4.111913772930216, 0.19223623526732384],
...  [0.009000000000000001, 4.505017235628538, 0.20666111673691043],
...  [0.01, 5.0961076665212595, 0.1259131288654157]]

>>> for row in measurements:
...     row[0] = '{:.1f}ms'.format(row[0]*1e3)
...     row[1] = '{:.1f}V'.format(row[1])
...     row[2] = '{:.0f}mA'.format(row[2]*1e3)

>>> header = ['Time', 'Voltage', 'Current']
>>> measurements.insert(0, header)

>>> print_table(measurements, '>')
  Time  Voltage  Current
 0.0ms     0.2V     58mA
 1.0ms     0.5V    104mA
 2.0ms     1.0V     63mA
 3.0ms     1.6V    163mA
 4.0ms     2.2V    166mA
 5.0ms     2.5V    185mA
 6.0ms     3.1V    249mA
 7.0ms     3.6V    199mA
 8.0ms     4.1V    192mA
 9.0ms     4.5V    207mA
10.0ms     5.1V    126mA

format string

Width and spacing

The colwidth parameter can be used to change column widths, which by default is just big enough to fit the contents. Setting it to 10, for instance, means that all columns are 10 characters wide. Setting it to [20, 10] means that the first column is 20 characters wide and the subsequent ones are 10. Unless all columns are specified, the last specified width is repeated for the remaining columns.

Content that is too long for its cell is truncated using the string suffix (default: '...'). Example:

>>> print_table(grades, colwidth=10)
            Math        English     History     Comment
Bob         1.2         2.1         5.9         Failed ...
Jane        2.4         1.1         1.4         Quite good
Trevor      2.2         4.4         3.2         Somewha...

The spacing between the columns is spacing characters (default: 2).

If the total table width exceeds maxwidth the column indicated by truncate (default: 0) is truncated on rows that are too long. If maxwidth is not specified it will be taken as the terminal width minus 1. This truncation overrides settings in colwidth.

Beware that no columns can have zero or negative width. If for instance maxwidth is 80 and colwidth is [10, 30, 30, 30] with spacing 2 the total width will initially be 10+2+30+2+30+2+30=106. That’s 26 characters too much, so a width of 26 will be removed from the truncated column. If truncate is 0, column 0 will have a width of -16 which is not permitted.

Example: Sorting a Table

Consider printing sorted table of the race times of a 10km run. The race times in seconds is already in a table, and we supply a separate header row:

>>> from frmt import format_time

>>> header =  ['Name'  , 'Time']
>>> race   = [['John'  , 3672  ],
...           ['Martha', 2879  ],
...           ['Stuart', 2934  ],
...           ['Eduard', 2592  ]]

>>> race.sort(key=lambda row: row[1])
>>> race.insert(0, header)

>>> print_table(race, '<>', format_time)
Name       Time
Eduard    43:12
Martha    47:59
Stuart    48:54
John    1:01:12

Example: Transposing a Table

A table can be transposed using zip along with the * operator:

>>> print_table(zip(*grades))
         Bob                Jane        Trevor
Math     1.2                2.4         2.2
English  2.1                1.1         4.4
History  5.9                1.4         3.2
Comment  Failed at history  Quite good  Somewhat average

zip(*grades), which is the equivalent of zip(grades[0], grades[1], grades[2], grades[3]), isn’t actually a list of lists. It is nonetheless an iterable of an iterable, and therefore perfectly understandable by *_table(). If you still want a list of list, e.g. for preprocessing the table, you could do list(map(list,zip(*grades))).

A common pattern is having a set of lists (or 1D NumPy arrays) and wanting to print them as columns. Here’s an example of that:

>>> time = [0.0, 0.001, 0.002, 0.003, 0.004, 0.005,
...         0.006, 0.007, 0.008, 0.009, 0.01]

>>> voltage = [0.16159999923218293, 0.5415871693699631, 1.0020586304683154,
...            1.6493888138044273, 2.158470579371153, 2.543489191597334,
...            3.1235687589204497, 3.6155358393212573, 4.111913772930216,
...            4.505017235628538, 5.0961076665212595]

>>> current = [0.05832942704771176, 0.1038533048639953, 0.06263011126285473,
...            0.1633588946456795, 0.16602352409683588, 0.18539040280004443,
...            0.24946423631204423, 0.19856685230794482,
...            0.19223623526732384, 0.20666111673691043, 0.1259131288654157]

>>> header = ['Time', 'Voltage', 'Current']
>>> measurements = list(zip(time, voltage, current))
>>> measurements.insert(0, header)

>>> print_table(measurements, '>', '{:.3f}')
 Time  Voltage  Current
0.000    0.162    0.058
0.001    0.542    0.104
0.002    1.002    0.063
0.003    1.649    0.163
0.004    2.158    0.166
0.005    2.543    0.185
0.006    3.124    0.249
0.007    3.616    0.199
0.008    4.112    0.192
0.009    4.505    0.207
0.010    5.096    0.126


Signature: *_time*(seconds)

*_time() represents time given in seconds using the format dd:hh:mm:ss when abs(seconds) >= 60 and using SI-prefixes and three significant figures otherwise. This gives a convenient resolution for the widest range of magnitudes. *_time_large() always uses the former format and *_time_small() always uses the latter. Rounding is taken care of. Examples:

>>> from frmt import print_time, print_time_small, print_time_large

>>> print_time(24*60*60)

>>> print_time(90)

>>> print_time(30)

>>> print_time(0.01255)

>>> print_time_small(90)

>>> print_time_large(30)

>>> print_time(float('nan'))


Signature: *_fit(text, width=None, align='<', suffix="...")

*_fit() fits a piece of text to width characters by truncating too long text and padding too short text with spaces. Truncation is indicated by a customizable suffix suffix (default: '...'). Examples:

>>> from frmt import format_fit

>>> format_fit('abcdefgh', 6) == 'abc...' # truncation

>>> format_fit('abcdefgh', 6, suffix='!') == 'abcde!' # truncation

>>> format_fit('abc', 6) == 'abc   ' # padding

The contents can be left, centered or right aligned by setting align to '<', '^' or '>', respectively:

>>> format_fit('abc', 6, '^') == ' abc  '

>>> format_fit('abc', 6, '>') == '   abc'

If width is not specified it is taken to be the terminal width. Hence print_fit(s) is equivalent to print(s) except that s will be truncated such as to not spill over to the next line in the terminal.

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