Python: Fixed length string multiple variables left/right aligned

Question

I am fairly new to Python and try to format a string for ouput on a LCD-display.

I would like to output a formatted table of train departures

the display has a fixed length of 20 characters (20x4)
I have 3 string-variables with variable length (line, station, eta)
2 of them should be left-aligned (line, station), while the third one should go right aligned

Example:

8: station A       8
45: long station  10
1: great station  25

I have played around with various things, but I am not able to define the max length for the overall string, but only 1 variable:

print('{0}: {1} {2:<20}'.format(line, station, eta))

Any tips and hints are much appreciated!

--- Solution based on @Rafael Cardoso s answer:

print(format_departure(line, station, eta))


def format_departure(line, station, eta):
    max_length = 20
    truncate_chars = '..'

    # add a leading space to the eta - just to be on the safe side
    eta = ' ' + eta

    output = '{0}: {1}'.format(line, station)  # aligns left

    # make sure that the first part is not too long, otherwise truncate
    if (len(output + eta)) > max_length:
        # shorten for truncate_chars + eta + space
        output = output[0:max_length - len(truncate_chars + eta)] + truncate_chars

    output = output + ' '*(max_length - len(output) - len(eta)) + eta  # aligns right

    return output

Have a look at tabulate: txt.arboreus.com/2013/03/13/pretty-print-tables-in-python.html (pypi.python.org/pypi/tabulate) — boardrider
– boardrider, Commented May 10, 2015 at 13:43

rafaelc · Accepted Answer · 2018-02-28 14:27:42Z

3

You can add spaces by making a calculation of how many spaces should be added in between station and eta :

>>> line = ['8', '45', '1']
>>> station = ['station A', 'long station', 'great station']
>>> eta = ['8','10', '25']
>>> MAX = 20

>>> for i in range(3):
    m_str = '{0}: {1}'.format(line[i], station[i]) #aligns left
    m_str = m_str + ' '*(MAX-len(str)-len(eta[i])) + eta[i] #aligns right
    print m_str

The calculation would be to get the max length (in this case 20) minus the current len of m_str minus what will yet come (len(eta[i])).

Bear in mind that it assumes that len(m_str) will not be greater than 20 at this point.

Output:

8: station A       8
45: long station  10
1: great station  25

edited Feb 28, 2018 at 14:27

answered May 9, 2015 at 13:31

rafaelc

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1 Comment

Nogga Over a year ago

I took your proposal and added some functionality to also account for line/station strings too long to display nicely.

Stefan Pochmann · Accepted Answer · 2015-05-09 13:52:20Z

1

Use a temporary string for the left part and its length:

tmp = '{}: {}'.format(line, station)
print('{}{:{}}'.format(tmp, eta, 20-len(tmp)))

Demo:

trains = ((8, 'station A', 8), (45, 'long station', 10), (1, 'great station', 25))
for line, station, eta in trains:
    tmp = '{}: {}'.format(line, station)
    print('{}{:{}}'.format(tmp, eta, 20-len(tmp)))

Prints:

8: station A       8
45: long station  10
1: great station  25

edited May 9, 2015 at 13:52

answered May 9, 2015 at 13:41

Stefan Pochmann

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Comments

krock · Accepted Answer · 2015-05-09 13:27:39Z

0

You can use slices to specify a max length. E.g. the following will only print the first 20 characters of the string resulting from the format:

print('{0}: {1} {2:<20}'.format(line, station, eta)[:20])

answered May 9, 2015 at 13:27

krock

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Comments

ZdaR · Accepted Answer · 2015-05-09 13:39:01Z

0

You can also use .rjust() and .ljust() methods on given strings to set their alignment,

lst = [[8, "station A", 8], [45, "long station", 10], [1, "great station", 25]]
for i in lst:
    print str(i[0]).ljust(2)+":"+i[1]+str(i[2]).rjust(20 - (len(i[1])+3))

Output:

8 :station A       8
45:long station   10
1 :great station  25

answered May 9, 2015 at 13:39

ZdaR

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Comments

Malik Brahimi · Accepted Answer · 2015-05-09 13:58:25Z

0

It seems to me that you wish to create a table, so I suggest you use prettytable like so:

from prettytable import PrettyTable

table = PrettyTable(['line', 'station', 'eta'])

table.add_row([8, 'station A', 10])
table.add_row([6, 'station B', 20])
table.add_row([5, 'station C', 15])

As it is not built in to Python, you will need to install it yourself from the package index here.

edited May 9, 2015 at 13:58

answered May 9, 2015 at 13:41

Malik Brahimi

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3 Comments

ZdaR Over a year ago

Don't we need to import something for prettyTable ?

Malik Brahimi Over a year ago

@anmol_uppal Thanks for the edit. What do you think of the library?

Nogga Over a year ago

You are right, but I prefer including as few libraries as possible

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