Question

可能重复：
Iterate an iterator by chunks (of n) in Python?

假设我有一个492个字符的字符串存储在一个变量中。如何打印前50个字符，然后转到下一行，然后打印出下一个50，最后打印一个包含42个字符的行？

Answer 1

chars_per_line = 50
for i in range(0, len(s), chars_per_line):
    print s[i:i+chars_per_line]

Answer 2

for line in mystring.splitlines():
    print line[:50]

Answer 3

In [363]: mystr = "A"*492

In [364]: print '\n'.join(mystr[i*width:(i+1)*width] for i in range(int(math.ceil(float(len(mystr))/width))))
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Answer 4

正如@Martijn Pieters暗示的那样，如果你有办法iterate an iterator by chunks (of n)，这将是非常容易的。如果您阅读了该问题，那么做就可以做到这一点。

所以，鉴于来自itertools recipes的grouper实施（或您偏好其他问题的其他任何内容）：

lines = [''.join(group) for group in grouper(50, my_string, '')]

或者，如果您只想将它们打印出来：

for group in grouper(50, my_string, ''):
    print ''.join(group)

一旦你知道grouper存在，我认为这比Joel Cornett的回答简单。请注意，他在第一个版本中没有工作，必须修复;这个几乎不可能出错。任何消除fencepost错误可能性的东西通常都会更好;这就是为什么我们有for - in循环和enumerate而不是C风格的for循环，等等。

这是在行动：

>>> my_string='1234567890'*49+'12'
>>> print my_string
123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012
>>> # That was ugly…
>>> for group in grouper(50, my_string, ''):
...     print ''.join(group)
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
12345678901234567890123456789012345678901234567890
123456789012345678901234567890123456789012
>>> # Pretty!

在Python中只打印一定数量的字符

4 个答案: