Powerful Python One-Liners
This page is devoted to short programs that can perform powerful operations called Python One-Liners.
You may ask: why should I care? The answer is profound: if you cannot read and write one-liner code snippets, how can you ever hope to read and write more complicated codebases? Python one-liners can be just as powerful as a long and tedious program written in another language designed to do the same thing. In other languages (think: Java) this would be nearly impossible, but in Python, it's a lot easier to do. The trick is to think of something that will "do a lot with a little." Most importantly, reading and writing about Python one-liners (e.g., in this post) is a lot of fun! There's even a whole subculture around who can write the shortest code for a given problem.
It would be awesome if this page expanded to the point where it needs some sort of organization system. (Edit: The one-liners are now sorted more or less by ease-of-understanding -- from simple to hard. Please use a "sorted insert" for your new one-liner.)
The source code is contributed from different Python coders --- Thanks to all of them! Special thanks to the early contributor JAM.
Of course, there is debate on whether one-liners are even Pythonic. As a rule of thumb: if you use one-liners that are confusing, difficult to understand, or to show off your skills, they tend to be Unpythonic. However, if you use well-established one-liner tricks such as list comprehension or the ternary operator, they tend to be Pythonic.
So, use your one-liner superpower wisely!
Free Python One-Liners Learning Resources
Python One-Line X - How to accomplish different tasks in a single line
Github '''Python One-Liners''' - Share your own one-liners with the community
Overview: 10 one-liners that fit into a tweet
I visited this page oftentimes and I loved studying the one-liners presented above. Thanks for creating this awesome resource, JAM, and RJW! 
Because I learned a lot from studying the one-liners, I thought why not revive the page (after almost ten years since the last change happened)?
After putting a lot of effort into searching the web for inspiration, I created the following ten one-liners. Some of them are more algorithmic (e.g. Quicksort). Some day, I will add a detailed explanation here - but for now, you can read this blog article to find explanations.
1 # Palindrome Python One-Liner
2 phrase.find(phrase[::-1])
3
4 # Swap Two Variables Python One-Liner
5 a, b = b, a
6
7 # Sum Over Every Other Value Python One-Liner
8 sum(stock_prices[::2])
9
10 # Read File Python One-Liner
11 [line.strip() for line in open(filename)]
12
13 # Factorial Python One-Liner
14 reduce(lambda x, y: x * y, range(1, n+1))
15
16 # Performance Profiling Python One-Liner
17 python -m cProfile foo.py
18
19 # Power set Python One-Liner
20 lambda l: reduce(lambda z, x: z + [y + [x] for y in z], l, [[]])
21
22 # Fibonacci Python One-Liner
23 lambda x: x if x<=1 else fib(x-1) + fib(x-2)
24
25 # Quicksort Python One-liner
26 lambda L: [] if L==[] else qsort([x for x in L[1:] if x< L[0]]) + L[0:1] + qsort([x for x in L[1:] if x>=L[0]])
27
28 # Sieve of Eratosthenes Python One-liner
29 reduce( (lambda r,x: r-set(range(x**2,n,x)) if (x in r) else r), range(2,int(n**0.5)), set(range(2,n)))
Find All Indices of an Element in a List
Say, you want to do the same as the list.index(element) method but return all indices of the element in the list rather than only a single one.
In this one-liner, you’re looking for element 'Alice' in the list lst = [1, 2, 3, 'Alice', 'Alice'] so it even works if the element is not in the list (unlike the list.index() method).
echo unicode character:
python -c "print unichr(234)"
This script echos "ê"
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
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 a 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).
Caution: Don't run this on your home directory or you're going to get all your text files edited.
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)]
Set of all subsets
- Function that returns the set of all subsets of its argument
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
Alternative (shorter, more functional version):
f = lambda l: reduce(lambda z, x: z + [y + [x] for y in z], l, [[]])
Terabyte to Bytes
Want to know many bytes a terabyte is? If you know further abbreviations, you can extend the list.
import pprint;pprint.pprint(zip(('Byte', 'KByte', 'MByte', 'GByte', 'TByte'), (1 << 10*i for i in range(5))))
Largest 8-Bytes Number
And what's the largest number that can be represented by 8 Bytes?
print '\n'.join("%i Byte = %i Bit = largest number: %i" % (j, j*8, 256**j-1) for j in (1 << i for i in range(8)))
Cute, isn't it?
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]";
Broadcast magic packet to power on wakeonlan enabled computer
Small Wikipedia Python script squeezed out to 166 characters length one-liner:
python -c "import socket as S;s=S.socket(S.AF_INET,S.SOCK_DGRAM);s.setsockopt(S.SOL_SOCKET,S.SO_BROADCAST,1);s.sendto(b'\xff'*6+b'\x84\x47\x09\x0b\x7f\xfd'*16,('<broadcast>',7))"
Uglier, with Python constant names replaced by their values, squeezed out to 123 characters only:
python -c "import socket as S;s=S.socket(2,2);s.setsockopt(1,6,1);s.sendto(b'\xff'*6+b'\x84\x47\x09\x0b\x7f\xfd'*16,('<broadcast>',9))"
Replace mac address \x84\x47\x09\x0b\x7f\xfd with mac address of computer that should be powered on.
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')))"
Print top 10 lines of stdin
python -c "import sys; sys.stdout.write(''.join(sys.stdin.readlines()[:10]))" < /path/to/your/file
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);"
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:
1 import sys,re
2
3 def main():
4 fh = open(sys.argv[1],'r')
5 lines = fh.readlines()
6 print '\tpython2.2 -c "`printf \\"if 1:\\n\\'
7 for line in lines:
8 line = re.sub('[\\\'\"()]','\\\g<0>',line)
9 # grab leading white space (should be multiples of 4) and makes them into
10 # tabs
11 wh_spc_len = len(re.match('\s*',line).group())
12
13 sys.stdout.write('\t')
14