Example tutorial of partition string function in Python-Python Tutorial-php.cn

Example tutorial of partition string function in Python

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Release： 2017-05-22 17:08:37

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In version 2.5Newadded a function called partition. What can it do? Give a small example:

>>> 'http://www.donews.net/limodou'.partition('://')
('http', '://', 'www.donews.net/limodou')
>>> 'file:/a.html'.partition('://')
('file:/ a.html', ”, ”)

## As can be seen from the first example, it is used to split the string according to the specified delimiter. If the string Contains the specified delimiter, returns a 3-element tuple, the first is the substring to the left of the delimiter, the second is the delimiter itself, and the third is the substring to the right of the delimiter. The second example shows that if the specified delimiter cannot be found, the return is still a 3-element tuple, the first one is the entire string, and the second and third are empty strings.

So someone may ask, what is the difference between it and split(sep, 1)? First of all, split may not return a fixed-length return value. It returns a

list. If it is found, it returns a 2-yuan list. If it is not found, it returns a 1-yuan list, such as:

>>> ‘a.b.c’.split(‘,’, 1)
[&#39;a.b.c&#39;]
>>> ‘a.b.c’.split(‘.’, 1)
[&#39;a&#39;, &#39;b.c&#39;]

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At the same time, it does not return the delimiter if found.

In some cases partition(sep) and rpartition(sep) (matching from right to left) have similar functions to split(sep, 1) and rsplit(sep, 1). However, partition is actually created to replace find and index, not split. In many cases, we need to find a location first and then split it. It is much more convenient to use partition. For example:

>>> a = ‘http://www.donews.net’
>>> pos = a.find(‘://’)
>>> if pos > -1:
…     print a[:pos], a[pos+1:]
http www.donews.net

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Is it simpler to use partition:

>>> a = ‘http://www.donews.net’
>>> left, sep, right = a.partition(‘://’)
>>> print left, right
http www.donews.net

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At the same time, in version 2.5, startswith and endswith have changed, and their first parameter can be a tuple. This is very convenient when judging several situations. For example, if you want to determine the file name suffix, when it originally only supported one value, you may have to split it first and then determine it. Endswith is not needed, such as:

>>> a = ‘a.gif’
>>> import os.path
>>> ext = os.path.splitext(a)[1]
>>> if ext in [&#39;.gif&#39;, &#39;.png&#39;, &#39;.bmp&#39;]:
…     print ‘found’
…
found

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But now you can:

>>> a = ‘a.gif’
>>> if a.endswith((‘.gif’, ‘png’, ‘.bmp’)):
…     print ‘found’
…
found

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Is that right? Much simpler. Note that the above tuple does not work if I replace it with a list. It seems to be mandatory.

Many interesting things are waiting for you and me to discover.

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