This sounds pretty basic but I ca't think of a neat straightforward method to do this in Python yet
I have a string like "abcdefgh" and I need to create a list of elements picking two characters at a time from the string to get ['ab','cd','ef','gh'].
What I am doing right now is this
output = []
for i in range(0,len(input),2):
output.append(input[i:i+2])
Is there a nicer way?
In [2]: s = 'abcdefgh'
In [3]: [s[i:i+2] for i in range(0, len(s), 2)]
Out[3]: ['ab', 'cd', 'ef', 'gh']
Just for the fun of it, if you hate for
>>> s='abcdefgh'
>>> map(''.join, zip(s[::2], s[1::2]))
['ab', 'cd', 'ef', 'gh']
Is there a nicer way?
Sure. List comprehension can do that.
def n_chars_at_a_time(s, n=2):
return [s[i:i+n] for i in xrange(0, len(s), n)]
should do what you want. The s[i:i+n] returns the substring starting at i and ending n characters later.
n_chars_at_a_time("foo bar baz boo", 2)
produces
['fo', 'o ', 'ba', 'r ', 'ba', 'z ', 'bo', 'o']
in the python REPL.
For more info see Generator Expressions and List Comprehensions:
Two common operations on an iterator’s output are
- performing some operation for every element,
- selecting a subset of elements that meet some condition.
For example, given a list of strings, you might want to strip off trailing whitespace from each line or extract all the strings containing a given substring.
List comprehensions and generator expressions (short form: “listcomps” and “genexps”) are a concise notation for such operations...
