如何对迭代器进行切片操作

这个题可以这样实现:
[code lang="pyton"]
f= open('sss','r').readlines()
f[100:300]

文件并不能直接进行切片操作。redlines()可以把每一行读入到一个列表中。
弊端，readlines()方法会一次性的把文件导入到内存当中，如果文件很大，那就尴尬了（内存不足）。

我们可以使用标准库下的itertools下的islice 方法

Python

In [74]: from <span class="wp_keywordlink_affiliate"><a href="https://www.168seo.cn/tag/itertools" title="View all posts in itertools" target="_blank">itertools</a></span> import <span class="wp_keywordlink_affiliate"><a href="https://www.168seo.cn/tag/islice" title="View all posts in islice" target="_blank">islice</a></span> In [75]: <span class="wp_keywordlink_affiliate"><a href="https://www.168seo.cn/tag/islice" title="View all posts in islice" target="_blank">islice</a></span>? Init signature: islice(self, /, *args, **kwargs) Docstring: islice(iterable, stop) --> islice object islice(iterable, start, stop[, step]) --> islice object Return an iterator whose next() method returns selected values from an iterable. If start is specified, will skip all preceding elements; otherwise, start defaults to zero. Step defaults to one. If specified as another value, step determines how many values are skipped between successive calls. Works like a slice() on a list but returns an iterator. Type: type In [76]: islice(f,0,10) Out[76]: <<span class="wp_keywordlink_affiliate"><a href="https://www.168seo.cn/tag/itertools" title="View all posts in itertools" target="_blank">itertools</a></span>.islice at 0x1055fe638> # 读取前十行 In [77]: islice(f,0,None) Out[77]: <<span class="wp_keywordlink_affiliate"><a href="https://www.168seo.cn/tag/itertools" title="View all posts in itertools" target="_blank">itertools</a></span>.islice at 0x1056014f8> # 从开头带结尾 In [78]: islice(f,10) Out[78]: <itertools.islice at 0x1055ae868> # 读取前十行 In [85]: l Out[85]: range(0, 10) In [86]: t = iter(l) In [87]: for x in islice(t,5,7): ...: print(x) ...: 5 6 #注意如果在用到迭代器,他会直接往下走,所以要用的时候注意下,你可以重新iter一个,这样就不会有问题了 In [88]: for x in t: ...: print(x) ...: ...: 7 8 9

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In [ 74 ] : from itertools import islice   In [ 75 ] : islice ? Init signature : islice ( self , / , * args , * * kwargs ) Docstring : islice ( iterable , stop ) -- > islice object islice ( iterable , start , stop [ , step ] ) -- > islice object   Return an iterator whose next ( ) method returns selected values from an iterable .    If start is specified , will skip all preceding elements ; otherwise , start defaults to zero .    Step defaults to one .    If specified as another value , step determines how many values are skipped between successive calls .    Works like a slice ( ) on a list but returns an iterator . Type :            type In [ 76 ] : islice ( f , 0 , 10 ) Out [ 76 ] : < itertools . islice at 0x1055fe638 > # 读取前十行     In [ 77 ] : islice ( f , 0 , None ) Out [ 77 ] : < itertools . islice at 0x1056014f8 > # 从开头带结尾   In [ 78 ] : islice ( f , 10 ) Out [ 78 ] : < itertools . islice at 0x1055ae868 > # 读取前十行     In [ 85 ] : l Out [ 85 ] : range ( 0 , 10 )   In [ 86 ] : t = iter ( l )   In [ 87 ] : for x in islice ( t , 5 , 7 ) :      . . . :      print ( x )      . . . : 5 6 #注意如果在用到迭代器,他会直接往下走,所以要用的时候注意下,你可以重新iter一个,这样就不会有问题了 In [ 88 ] : for x in t :      . . . :      print ( x )      . . . :      . . . : 7 8 9

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