Share python string learning summary

Indexand sharding:

1. Index: s[j] Get the element at a specific offset

Note: There are positive and negative offsets Offset

Negative offset is counting from the end or the right in reverse direction

The negative index number plusThe length of the stringis equal to the position of the positive offset

2. Commonly used methods of sharding:

s[i:j] means starting from the element at the i-th position and ending at the j-th position, excluding the j-th element. Element (left closed, right open)

s[1:] Get all elements starting from offset 1, including elements at position 1

s[:3] Get Starting from offset 0, to the element at offset 3, excluding the element at position 3

s[:-1] Gets all elements starting from offset 0, excluding the last element

s[:] Copy the entire string

3. Extended sharding, the third limit value:

pythonIn 2.3, shardingExpressionAdd an optional third index, used as a step

s[x:y:z] means, starting from the x position, to the offset y The position element (excluding y position), where the interval is z, take out the elements

4, sliceobjectslice()

>>>s = 'spam'

>>>s[1:3]

>>>'pa'

>>>s [slice(1,3)]

>>>'pa'

5. The role of slicing:

(1) A slicing expression Able to return a list of all elements except the first one

(2) Clean the contents of the input file

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