String indexing and sharding in Python

1. The index of the string

gives a string and can output any character. If the index is a negative number, it is equivalent to counting from back to front.

>>> str="HelloWorld!"

>>> print str[0]

H

>>> print str[-4]

r

>>> str="HelloWorld!"

>>> print str[0]

H

>>> print str[-4]

r

2. Slicing of strings

Slicing is to separate parts from a given string content.

>>> str="HelloWorld!"

>>> print str[0]

H

>>> print str[-4]

r

>>> print str[1:4]

ell

>>> print str[:-7]

Hell

>>> print str[5:]

World!

>>> str="HelloWorld!"

>>> print str[0]

H

>>> print str[-4]

r

>>> print str[1:4]

ell

>>> print str[:-7]

Hell

>>> print str[5:]

World!

Extended form of sharding:

str[I,J,K] means from I to J-1, indexing every K elements , if K is a negative number, it is indexed from left to right.

>>> print str[2:7:2]

loo

>>> print str[2:7:1]

lloWo

>>> print str[2:7:2]

loo

>>> print str[2:7:1]

lloWo

ord function converts characters into corresponding ASCII code values, while chr function converts numbers into characters. For example:

>>> print ord('a')

97

>>> print chr(97)

a

>>>

>>> print ord('a')

97

>>> print chr(97)

a

>>>

Modifying a string in Python can only be reassigned.

Every time a string is modified, a new string object is generated, which seems to cause a decrease in efficiency. In fact, Python will automatically garbage collect strings that are no longer used, so

The object reuses space previously occupied by a string.

String formatting:

>>> "%d %s %d you!"%(1,"goujinping",8)

'1 goujinping 8 you!'

>>> " %d %s %d you!"%(1,"goujinping",8)

'1 goujinping 8 you!'