Formatting a list of text into columns

Question

I'm trying to output a list of string values into a 2 column format. The standard way of making a list of strings into "normal text" is by using the string.join method. However, it only takes 2 arguments so I can only make a single column using "\n". I thought trying to make a loop that would simply add a tab between columns would do it but the logic didn't work correctly.

I found an ActiveState page that has a fairly complicated way of doing it but it's from 4 years ago. Is there an easy way to do it nowadays?

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Edit Here is the list that I want to use.

skills_defs = ["ACM:Aircraft Mechanic", "BC:Body Combat", "BIO:Biology",
    "CBE:Combat Engineer", "CHM:Chemistry", "CMP:Computers", 
    "CRM:Combat Rifeman", "CVE:Civil Engineer", "DIS:Disguise",
    "ELC:Electronics","EQ:Equestrian", "FO:Forward Observer",
    "FOR:Forage", "FRG:Forgery", "FRM:Farming", "FSH:Fishing",
    "GEO:Geology", "GS:Gunsmith", "HW:Heavy Weapons", "IF:Indirect Fire",
    "INS:Instruction", "INT:Interrogation", "JP:Jet Pilot", "LB:Longbow",
    "LAP:Light Aircraft Pilot", "LCG:Large Caliber Gun", "LNG:Language",
    "LP:Lockpick", "MC:Melee Combat", "MCY:Motorcycle", "MEC:Mechanic",
    "MED:Medical", "MET:Meterology", "MNE:Mining Engineer",
    "MTL:Metallurgy", "MTN:Mountaineering", "NWH:Nuclear Warhead",
    "PAR:Parachute", "PST:Pistol", "RCN:Recon", "RWP:Rotary Wing Pilot",
    "SBH:Small Boat Handling","SCD:Scuba Diving", "SCR:Scrounging",
    "SWM:Swimming", "TW:Thrown Weapon", "TVD:Tracked Vehicle Driver",
    "WVD:Wheeled Vehicle Driver"]

I just want to output this list into a simple, 2 column format to reduce space. Ideally there should be a standard amount of space between the columns but I can work with it.

ACM:Aircraft Mechanic     BC:Body Combat 
BIO:Biology   CBE:Combat Engineer 
CHM:Chemistry    CMP:Computers
CRM:Combat Rifeman   CVE:Civil Engineer 
DIS:Disguise      ELC:Electronics 
EQ:Equestrian     FO:Forward Observer
FOR:Forage    FRG:Forgery 
FRM:Farming       FSH:Fishing
GEO:Geology       GS:Gunsmith 
HW:Heavy Weapons     IF:Indirect Fire
INS:Instruction       INT:Interrogation 
JP:Jet Pilot      LB:Longbow
 LAP:Light Aircraft Pilot    LCG:Large Caliber Gun 
LNG:Language      LP:Lockpick 
MC:Melee Combat      MCY:Motorcycle 
MEC:Mechanic      MED:Medical 
MET:Meterology   MNE:Mining Engineer
MTL:Metallurgy   MTN:Mountaineering 
NWH:Nuclear Warhead  PAR:Parachute 
PST:Pistol    RCN:Recon 
RWP:Rotary Wing Pilot    SBH:Small Boat Handling 
SCD:Scuba Diving     SCR:Scrounging
SWM:Swimming     TW:Thrown Weapon 
TVD:Tracked Vehicle Driver  WVD:Wheeled Vehicle Driver

Answer 1

data = [ ("1","2"),("3","4") ]
print "\n".join(map("\t".join,data))

Not as flexible as the ActiveState solution, but shorter :-)

Answer 2

Two columns, separated by tabs, joined into lines. Look in itertools for iterator equivalents, to achieve a space-efficient solution.

import string
def fmtpairs(mylist):
    pairs = zip(mylist[::2],mylist[1::2])
    return '\n'.join('\t'.join(i) for i in pairs)

print fmtpairs(list(string.ascii_uppercase))

A   B
C   D
E   F
G   H
I   J
...

Oops... got caught by S.Lott (thank you).

A more general solution, handles any number of columns and odd lists. Slightly modified from S.lott, using generators to save space.

def fmtcols(mylist, cols):
    lines = ("\t".join(mylist[i:i+cols]) for i in xrange(0,len(mylist),cols))
    return '\n'.join(lines)

Answer 3

It's long-winded, so I'll break it into two parts.

def columns( skills_defs, cols=2 ):
    pairs = [ "\t".join(skills_defs[i:i+cols]) for i in range(0,len(skills_defs),cols) ]
    return "\n".join( pairs )

It can, obviously, be done as a single loooong statement.

This works for an odd number of skills, also.

Answer 4

The format_columns function should do what you want:

from __future__ import generators
try: import itertools
except ImportError: mymap, myzip= map, zip
else: mymap, myzip= itertools.imap, itertools.izip

def format_columns(string_list, columns, separator=" "):
    "Produce equal-width columns from string_list"
    sublists= []

    # empty_str based on item 0 of string_list
    try:
        empty_str= type(string_list[0])()
    except IndexError: # string_list is empty
        return

    # create a sublist for every column
    for column in xrange(columns):
            sublists.append(string_list[column::columns])

    # find maximum length of a column
    max_sublist_len= max(mymap(len, sublists))

    # make all columns same length
    for sublist in sublists:
         if len(sublist) < max_sublist_len:
             sublist.append(empty_str)

    # calculate a format string for the output lines
    format_str= separator.join(
        "%%-%ds" % max(mymap(len, sublist))
         for sublist in sublists)

    for line_items in myzip(*sublists):
        yield format_str % line_items

if __name__ == "__main__":
    skills_defs = ["ACM:Aircraft Mechanic", "BC:Body Combat", "BIO:Biology",
        "CBE:Combat Engineer", "CHM:Chemistry", "CMP:Computers",
        "CRM:Combat Rifeman", "CVE:Civil Engineer", "DIS:Disguise",
        "ELC:Electronics","EQ:Equestrian", "FO:Forward Observer",
        "FOR:Forage", "FRG:Forgery", "FRM:Farming", "FSH:Fishing",
        "GEO:Geology", "GS:Gunsmith", "HW:Heavy Weapons", "IF:Indirect Fire",
        "INS:Instruction", "INT:Interrogation", "JP:Jet Pilot", "LB:Longbow",
        "LAP:Light Aircraft Pilot", "LCG:Large Caliber Gun", "LNG:Language",
        "LP:Lockpick", "MC:Melee Combat", "MCY:Motorcycle", "MEC:Mechanic",
        "MED:Medical", "MET:Meterology", "MNE:Mining Engineer",
        "MTL:Metallurgy", "MTN:Mountaineering", "NWH:Nuclear Warhead",
        "PAR:Parachute", "PST:Pistol", "RCN:Recon", "RWP:Rotary Wing Pilot",
        "SBH:Small Boat Handling","SCD:Scuba Diving", "SCR:Scrounging",
        "SWM:Swimming", "TW:Thrown Weapon", "TVD:Tracked Vehicle Driver",
        "WVD:Wheeled Vehicle Driver"]

    for line in format_columns(skills_defs, 2):
        print line

This assumes that you have a Python with generators available.