Python advanced features-Slice ),

Python advanced features-Slice ),

Define a list:

1	L = ['haha','xixi','hehe','heihei','gaga']

Take the first three elements:

>>> L[0],L[1],L[2]('haha', 'xixi', 'hehe')

This method is a bit silly, because if there are many elements, we need to take the first N of them. What should we do?

You may think of loop:

>>> r=[]>>> n = 3>>> for i in range(n):...     r.append(L[i])...>>> r['haha', 'xixi', 'hehe']

However, similar to this frequently-used operation method, almost all languages provide simple operation methods, similar to the Substring method (commonly known as getting substrings ), python also provides a similar method, which is Slice ).

For example:

>>> L[0:3]['haha', 'xixi', 'hehe']

Here, L [0: 3] indicates that index 3 is known from index 0, but does not include index 3, that is, index 0, 1, 2.

If the first index is 0, it can also be omitted:

>>> L[:3]['haha', 'xixi', 'hehe']

You can also start with any index:

>>> L[1:2]['xixi']

You can also try:

>>> L[1:1][]

Because Python also supports the reciprocal number L [-1], let's see if it supports reciprocal slice: (remember, the first last index is-1)

>>> L[-2:]['heihei', 'gaga']

>>> L[-3:-2]['hehe']

If you are not satisfied, continue with the following:

>>> M = list (range (100) # create a series from 0 to 99 using the range Function to form a list value assigned to m >>> m [0, 1, 2, 3, 4, 5, 6 ,......, 99]

>>> M [: 10] # obtain the top 10 numbers [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> m [-10:] # obtain the last ten numbers [90, 91, 92, 93, 94, 95, 96, 97, 98, 99] >>> m [10: 20] # obtain the first 11-20 numbers [10, 11, 12, 13, 14, 15, 16, 17, 18, 19] >>> m [: 10: 2] # in the top 10, take one [0, 2, 4, 6, 8] >>> m [] # In the number 6-15, one [5, 8, 11, 14] for each 3] >>> m [:: 10] # In all the numbers, take one [0, 10, 20, 30, 40, 50, 60, 70, 80, 90] for each 10 numbers >>> m [:] # Do not write anything. You can copy a list [0, 1, 2, 3, 4, 5, 6, 7,…, as is ,......, 99]

Tuple also supports the slicing feature, but the result is also a tuple:

>>> n = (1,3,5,7)>>> n[:3](1, 3, 5)

Let's take a look at the string:

>>> 'abcdefghjklmn'[::2]'acegjln'

The string also supports slicing, but the result is also a string.

Let's look at another example:

Using the slicing function, write a function trim (str), similar to the strip () function in Python -- remove spaces at the beginning and end of a string:

>>> def trim(str):...     while str[:1]==' ':...             str = str[1:]...     while str[-1:] == ' ':...             str = str[:-2]...     return str...>>> trim('  abc  hh  welcome!      ')'abc  hh  welcome!'