通过子字符串进行类型化循环

Question

我有一个子串：

a="this is a really big long string which i am going to print substrings from"

我想打印它，然后打印a0:-6；a0:-12；a0:-18；依此类推，直到打印的子字符串为空。我如此喜欢python的部分原因是，你通常可以让你的循环看起来比其他语言中的更好，但我想不出一种方法来做到这一点。

Answer 1

由于这里的所有答案在核心上都是相等的，让我就所做的步骤给出一些简短的解释。当谈到pythonian式的做事方式时，大多数时候(当然不是完全)指的是list comprehension。在您的例子中，您可以使用它，如下所示：

[a[i] for i in range(0,len(a),1)]

您可以遍历字符串中的每个字符。如果您希望始终具有长度为6的子字符串，那么它将是

[a[i:i+6] for i in range(0,len(a)-6,1)]

注意:您需要关注字符串len(a)-6`的上限

Since you want your substring to always start at position 0 we fixate it with ```
a[0:...]

最后，我们使用i通过-6的步骤从end len(a)转到start 0

a="this is a really big long string which i am going to print substrings from"

[a[0:i] for i in range(len(a),0,-6)]

-->
['this is a really big long string which i am going to print substrings from',
 'this is a really big long string which i am going to print substring',
 'this is a really big long string which i am going to print sub',
 'this is a really big long string which i am going to pri',
 'this is a really big long string which i am going ',
 'this is a really big long string which i am ',
 'this is a really big long string which',
 'this is a really big long string',
 'this is a really big long ',
 'this is a really big',
 'this is a real',
 'this is ',
 'th']

现在，它返回子字符串的列表。如果你想直接打印它们，我们使用另一个技巧，那就是

def func(a, b, c):
  [...]

l = [a, b, c]

func(*l) == func(a, b, c)

我们可以使用asterix *解压一个列表，以便将参数传递给函数，因此我们还可以将列表中的每个子字符串传递给print函数。然而，在默认情况下，打印的分隔符是一个空格，所以我们需要用sep=\n"来改变它

print(*[a[0:i] for i in range(len(a),0,-6)],sep="\n")

print(*[a[0:i] for i in range(len(a),0,-6)],sep="\n")
this is a really big long string which i am going to print substrings from
this is a really big long string which i am going to print substring
this is a really big long string which i am going to print sub
this is a really big long string which i am going to pri
this is a really big long string which i am going 
this is a really big long string which i am 
this is a really big long string which
this is a really big long string
this is a really big long 
this is a really big
this is a real
this is 
th

Answer 2

使用for循环：

a = "this is a really big long string which i am going to print substrings from"

for i in range(0, -len(a), -6):
    b = a[:i]
    print(b)

输出：

this is a really big long string which i am going to print substring
this is a really big long string which i am going to print sub
this is a really big long string which i am going to pri
this is a really big long string which i am going 
this is a really big long string which i am 
this is a really big long string which
this is a really big long string
this is a really big long 
this is a really big
this is a real
this is 
th

下面是一个列表理解方法：

a = "this is a really big long string which i am going to print substrings from"

print('\n'.join(a[:i] for i in range(0, -len(a), -6)))

Answer 3

试着这样做：

print(*reversed([a[0:x] for x in range(0,len(a)-6,6)]),sep="\n")

输出：

this is a really big long string which i am going to print substri
this is a really big long string which i am going to print s
this is a really big long string which i am going to p
this is a really big long string which i am goin
this is a really big long string which i a
this is a really big long string whi
this is a really big long stri
this is a really big lon
this is a really b
this is a re
this i