Python itertools

╰半橙微兮° 2022-01-14 11:13 202阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

**Infinite iterators:**

**Iterators terminating on the shortest input sequence:**

<table> 
 <tbody> 
  <tr> 
   <th>Iterator</th> 
   <th>Arguments</th> 
   <th>Results</th> 
   <th>Example</th> 
  </tr> 
 </tbody> 
 <tbody> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.accumulate" rel="nofollow"><code>accumulate()</code></a></td> 
   <td>p [,func]</td> 
   <td>p0, p0+p1, p0+p1+p2, …</td> 
   <td><code>accumulate([1,2,3,4,5])&nbsp;--&gt;&nbsp;1&nbsp;3&nbsp;610&nbsp;15</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.chain" rel="nofollow"><code>chain()</code></a></td> 
   <td>p, q, …</td> 
   <td>p0, p1, … plast, q0, q1, …</td> 
   <td><code>chain('ABC',&nbsp;'DEF')&nbsp;--&gt;&nbsp;A&nbsp;B&nbsp;C&nbsp;D&nbsp;EF</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.chain.from_iterable" rel="nofollow"><code>chain.from_iterable()</code></a></td> 
   <td>iterable</td> 
   <td>p0, p1, … plast, q0, q1, …</td> 
   <td><code>chain.from_iterable(['ABC','DEF'])&nbsp;--&gt;&nbsp;A&nbsp;B&nbsp;C&nbsp;D&nbsp;E&nbsp;F</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.compress" rel="nofollow"><code>compress()</code></a></td> 
   <td>data, selectors</td> 
   <td>(d[0] if s[0]), (d[1] if s[1]), …</td> 
   <td><code>compress('ABCDEF',&nbsp;[1,0,1,0,1,1])--&gt;&nbsp;A&nbsp;C&nbsp;E&nbsp;F</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.dropwhile" rel="nofollow"><code>dropwhile()</code></a></td> 
   <td>pred, seq</td> 
   <td>seq[n], seq[n+1], starting when pred fails</td> 
   <td><code>dropwhile(lambda&nbsp;x:&nbsp;x&lt;5,[1,4,6,4,1])&nbsp;--&gt;&nbsp;6&nbsp;4&nbsp;1</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.filterfalse" rel="nofollow"><code>filterfalse()</code></a></td> 
   <td>pred, seq</td> 
   <td>elements of seq where pred(elem) is false</td> 
   <td><code>filterfalse(lambda&nbsp;x:&nbsp;x%2,range(10))&nbsp;--&gt;&nbsp;0&nbsp;2&nbsp;4&nbsp;6&nbsp;8</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.groupby" rel="nofollow"><code>groupby()</code></a></td> 
   <td>iterable[, key]</td> 
   <td>sub-iterators grouped by value of key(v)</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.islice" rel="nofollow"><code>islice()</code></a></td> 
   <td>seq, [start,] stop [, step]</td> 
   <td>elements from seq[start:stop:step]</td> 
   <td><code>islice('ABCDEFG',&nbsp;2,&nbsp;None)&nbsp;--&gt;&nbsp;CD&nbsp;E&nbsp;F&nbsp;G</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.starmap" rel="nofollow"><code>starmap()</code></a></td> 
   <td>func, seq</td> 
   <td>func(*seq[0]), func(*seq[1]), …</td> 
   <td><code>starmap(pow,&nbsp;[(2,5),&nbsp;(3,2),(10,3)])&nbsp;--&gt;&nbsp;32&nbsp;9&nbsp;1000</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.takewhile" rel="nofollow"><code>takewhile()</code></a></td> 
   <td>pred, seq</td> 
   <td>seq[0], seq[1], until pred fails</td> 
   <td><code>takewhile(lambda&nbsp;x:&nbsp;x&lt;5,[1,4,6,4,1])&nbsp;--&gt;&nbsp;1&nbsp;4</code></td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.tee" rel="nofollow"><code>tee()</code></a></td> 
   <td>it, n</td> 
   <td>it1, it2, … itn splits one iterator into n</td> 
   <td>&nbsp;</td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.zip_longest" rel="nofollow"><code>zip_longest()</code></a></td> 
   <td>p, q, …</td> 
   <td>(p[0], q[0]), (p[1], q[1]), …</td> 
   <td><code>zip_longest('ABCD',&nbsp;'xy',fillvalue='-')&nbsp;--&gt;&nbsp;Ax&nbsp;By&nbsp;C-&nbsp;D-</code></td> 
  </tr> 
 </tbody> 
</table>

**Combinatoric iterators:**

<table> 
 <tbody> 
  <tr> 
   <th>Iterator</th> 
   <th>Arguments</th> 
   <th>Results</th> 
  </tr> 
 </tbody> 
 <tbody> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.product" rel="nofollow"><code>product()</code></a></td> 
   <td>p, q, … [repeat=1]</td> 
   <td>cartesian product, equivalent to a nested for-loop</td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.permutations" rel="nofollow"><code>permutations()</code></a></td> 
   <td>p[, r]</td> 
   <td>r-length tuples, all possible orderings, no repeated elements</td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.combinations" rel="nofollow"><code>combinations()</code></a></td> 
   <td>p, r</td> 
   <td>r-length tuples, in sorted order, no repeated elements</td> 
  </tr> 
  <tr> 
   <td><a href="https://docs.python.org/3/library/itertools.html#itertools.combinations_with_replacement" rel="nofollow"><code>combinations_with_replacement()</code></a></td> 
   <td>p, r</td> 
   <td>r-length tuples, in sorted order, with repeated elements</td> 
  </tr> 
  <tr> 
   <td><code>product('ABCD',&nbsp;repeat=2)</code></td> 
   <td>&nbsp;</td> 
   <td><code>AA&nbsp;AB&nbsp;AC&nbsp;AD&nbsp;BA&nbsp;BB&nbsp;BC&nbsp;BD&nbsp;CA&nbsp;CB&nbsp;CC&nbsp;CD&nbsp;DA&nbsp;DB&nbsp;DCDD</code></td> 
  </tr> 
  <tr> 
   <td><code>permutations('ABCD',&nbsp;2)</code></td> 
   <td>&nbsp;</td> 
   <td><code>AB&nbsp;AC&nbsp;AD&nbsp;BA&nbsp;BC&nbsp;BD&nbsp;CA&nbsp;CB&nbsp;CD&nbsp;DA&nbsp;DB&nbsp;DC</code></td> 
  </tr> 
  <tr> 
   <td><code>combinations('ABCD',&nbsp;2)</code></td> 
   <td>&nbsp;</td> 
   <td><code>AB&nbsp;AC&nbsp;AD&nbsp;BC&nbsp;BD&nbsp;CD</code></td> 
  </tr> 
  <tr> 
   <td><code>combinations_with_replacement('ABCD',2)</code></td> 
   <td>&nbsp;</td> 
   <td><code>AA&nbsp;AB&nbsp;AC&nbsp;AD&nbsp;BB&nbsp;BC&nbsp;BD&nbsp;CC&nbsp;CD&nbsp;DD</code></td> 
  </tr> 
 </tbody> 
</table>

转载于:https://my.oschina.net/redhands/blog/3018499

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/1d572d72d2ef4472966b88fe8605a295.png