Utilize Functions (4.5-4.5.2) - Deutschina's Tech Diary

In Python, function itself can be a parameter of functions.

>>> sent = ['Take', 'care', 'of', 'the', 'sense', ',', 'and', 'the', 
...     'sounds', 'will', 'take', 'care', 'of', 'themselves', '.']
>>> def extract_property(prop):
...     return [prop(word) for word in sent]
... 
>>> extract_property(len)
[4, 4, 2, 3, 5, 1, 3, 3, 6, 4, 4, 4, 2, 10, 1]
>>> 
>>> def last_letter(word):
...     return word[-1]
... 
>>> extract_property(last_letter)
['e', 'e', 'f', 'e', 'e', ',', 'd', 'e', 's', 'l', 'e', 'e', 'f', 's', '.']
>>>

The next example is same behavior as last_letter() above.

>>> extract_property(lambda w: w[-1])
['e', 'e', 'f', 'e', 'e', ',', 'd', 'e', 's', 'l', 'e', 'e', 'f', 's', '.']

Option of sort(). First 2 examples are same. "cmp" option is default and can be omitted. The last one is descending sorted by length.

>>> sorted(sent)
[',', '.', 'Take', 'and', 'care', 'care', 'of', 'of', 'sense', 'sounds', 'take', 'the', 'the', 'themselves', 'will']
>>> sorted(sent, cmp)
[',', '.', 'Take', 'and', 'care', 'care', 'of', 'of', 'sense', 'sounds', 'take', 'the', 'the', 'themselves', 'will']
>>> sorted(sent, lambda x, y: cmp(len(y), len(x)))
['themselves', 'sounds', 'sense', 'Take', 'care', 'will', 'take', 'care', 'the', 'and', 'the', 'of', 'of', ',', '.']
>>>

The result of search1() and search2() are same.

>>> def search1(substring, words):
...     result = []
...     for word in words:
...             if substring in word:
...                     result.append(word)
...     return result
... 
>>> def search2(substring, words):
...     for word in words:
...             if substring in word:
...                     yield word
... 
>>> for item in search1('zz', nltk.corpus.brown.words()):
...     print item
... 
Grizzlies'
fizzled
....

The difference can be seen when try followings.

>>> search2('zz', nltk.corpus.brown.words())
&lt;generator object search2 at 0x1024acd70>
>>> searchi('zz', nltk.corpus.brown.words())
["Grizzlies'", 'fizzled', 'Rizzuto', 'huzzahs', 'dazzler', 
....

This function is to display all combinations of listed words.

>>> def permutations(seq):
...     if len(seq) &lt;= 1:
...             yield seq
...     else:
...             for perm in permutations(seq[1:]):
...                     for i in range(len(perm) + 1):
...                             yield perm[:i] + seq[0:1] + perm[i:]
... 
>>> list(permutations(['police', 'fish', 'buffalo']))
[['police', 'fish', 'buffalo'], ['fish', 'police', 'buffalo'], ['fish', 'buffalo', 'police'], ['police', 'buffalo', 'fish'], ['buffalo', 'police', 'fish'], ['buffalo', 'fish', 'police']]