Powerful Python One-Liners

This is a page that is devoted to short programs that can perform powerful operations. The ability to write short programs that are just as powerful as a program written in another language designed to do the same thing. However, it is sometimes fun to try and write a program in Python that is only one line. In other languages this would be nearly impossible, but in Python it is a lot easier to do. The trick is to think up something that will "do a lot with a little." I, personally, would love to see this page expanded to the point where it needs some sort of organization system.

Thanks for Your Code, JAM

Of course, there is debate on whether one-liners are even Pythonic.

Contributed Code

Some thoughts by ewo:

import pprint;pprint.pprint(zip(('Byte', 'KByte', 'MByte', 'GByte', 'TByte'), (1 << 10*i for i in xrange(5))))

print '\n'.join("%i Byte = %i Bit = largest number: %i" % (j, j*8, 256**j-1) for j in (1 << i for i in xrange(8)))

Cute, isn't it?

Set of all subsets

f = lambda x: [[y for j, y in enumerate(set(x)) if (i >> j) & 1] for i in range(2**len(set(x)))]

>>>f([10,9,1,10,9,1,1,1,10,9,7])
[[], [9], [10], [9, 10], [7], [9, 7], [10, 7], [9, 10, 7], [1], [9, 1], [10, 1], [9, 10, 1], [7, 1], [9, 7, 1], [10, 7, 1], [9, 10, 7, 1]]

-RJW

Alternately (shorter, more functional version):

f = lambda l: reduce(lambda z, x: z + [y + [x] for y in z], l, [[]])

Decode a base64 encoded file

import base64, sys; base64.decode(open(sys.argv[1], "rb"), open(sys.argv[2], "wb"))

Editing a list of files in place

I came up with this one-liner in response to an article that said it couldn't be done as an one-liner in Python.

What this does is replace the substring "at" by "op" on all lines of all files (in place) under the path specified (here, the current path).

   1 import sys,os,re,fileinput;a=[i[2] for i in os.walk('.') if i[2]] [0];[sys.stdout.write(re.sub('at','op',j)) for j in fileinput.input(a,inplace=1)]

Clearer is: import os.path; a=[f for f in os.listdir('.') if not os.path.isdir(f)]

Reimplementing cut

Print every line from an input file but remove the first two fields.

python -c "import sys;[sys.stdout.write(' '.join(line.split(' ')[2:])) for line in sys.stdin]" < input.txt

Cramming Python into Makefiles

A related issue is embedding Python into a Makefile. I had a really long script that I was trying to cram into a makefile so I automated the process:

import sys,re

def main():
    fh = open(sys.argv[1],'r')
    lines = fh.readlines()
    print '\tpython2.2 -c "`printf \\"if 1:\\n\\'
    for line in lines:
        line = re.sub('[\\\'\"()]','\\\g<0>',line)
        # grab leading white space (should be multiples of 4) and makes them into
        # tabs
        wh_spc_len = len(re.match('\s*',line).group())

        sys.stdout.write('\t')
        sys.stdout.write(wh_spc_len/4*'\\t'+line.rstrip().lstrip())
        sys.stdout.write('\\n\\\n')
    print '\t\\"`"'

if __name__=='__main__':
    main()

This script generates a "one-liner" from make's point of view.

echo unicode character:

python -c "print unichr(234)"

This script echos "ê"

Apply regular expression to lines from stdin

[another command] | python -c "import sys,re;[sys.stdout.write(re.sub('PATTERN', 'SUBSTITUTION', line)) for line in sys.stdin]"

Modify lines from stdin using map

python -c "import sys; tmp = lambda x: sys.stdout.write(x.split()[0]+'\t'+str(int(x.split()[1])+1)+'\n'); map(tmp, sys.stdin);"

Display List of all users on Unix-like systems

print '\n'.join(line.split(":",1)[0] for line in open("/etc/passwd"))

CSV file to json

python -c "import csv,json;print json.dumps(list(csv.reader(open('csv_file.csv'))))"

Compress CSS file

python -c 'import re,sys;print re.sub("\s*([{};,:])\s*", "\\1", re.sub("/\*.*?\*/", "", re.sub("\s+", " ", sys.stdin.read())))'

Decode string written in Hex

python -c "print ''.join(chr(int(''.join(i), 16)) for i in zip(*[iter('474e552773204e6f7420556e6978')]*2))"

Retrieve content text from HTTP data

python -c "import sys; print sys.stdin.read().replace('\r','').split('\n\n',2)[1]";

Prints file extension

print '~/python/one-liners.py'.split('.')[-1]

Escapes content from stdin

This can be used to convert a string into a "url safe" string

python -c "import urllib, sys ; print urllib.quote_plus(sys.stdin.read())";

Reverse lines in stdin

python -c "import sys; print '\n'.join(reversed(sys.stdin.read().split('\n')))"

python -c "import sys; sys.stdout.write(''.join(sys.stdin.readlines()[:10]))" < /path/to/your/file

Sony's Open Source command line tool for performing python one liners using unix-like pipes

They call it "The Pyed Piper" or pyp. It's pretty similar to the -c way of executing python, but it imports common modules and has it's own preset variable that help with splitting/joining, line counter, etc. You use pipes to pass information forward instead of nested parentheses, and then use your normal python string and list methods. Here is an example from the homepage:

Here, we take a linux long listing, capture every other of the 5th through the 10th lines, keep username and file name fields, replace "hello" with "goodbye", capitalize the first letter of every word, and then add the text "is splendid" to the end:

ls -l | pyp "pp[5:11:2] | whitespace[2], w[-1] | p.replace('hello','goodbye') | p.title(),'is splendid'"

and the explanation:

This uses pyp's built-in string and list variables (p and pp), as well as the variable whitespace and it's shortcut w, which both represent a list based on splitting each line on whitespace (whitespace = w = p.split()). The other functions and selection techniques are all standard python. Notice the pipes ("|") are inside the pyp command.

http://code.google.com/p/pyp/ http://opensource.imageworks.com/?p=pyp

Powerful Python One-Liners (last edited 2012-08-18 13:35:55 by aepj25)

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