Python 学习（六）

Assignment Statements

Assignments create object references.

Names are created when first assigned.

Names nust be assigned before being referenced.

Some operations perform assignments implicitly.

Augmented Assignments 增量赋值

Augmented assignment and shared reference.

+=really means extend

变量命名规则

Variable Name Rules

Syntax:(underscore or lette)+(any number of letters,digits,or underscores)

Variable names must start with an underscore or letter,which can be followed by any

number of letters ,digits,or underscores.

Case matters:

Reserved words are off-lim its

print 函数正则表达式:

print([object,...][,sep=''][,end='\n'][,file=sys.stdout])

If you assing them this way:

A=B=C=[]

all three names reference the same object,so changing it in-place from one

(e.g.,A.append(99))will affect the others .This is true only for in-place changes to

mutable objects like lists and dictionaries; for immutable objects such as numbers

and strings,this issue is irrelevant.