Detailed explanation of Python process control code

1.whileStatement

Condition LoopControl statement. Generally, it needs to be used together with break, otherwise it will enter an infinite loop.

Format: [ while ：

                                                                                                             if

statement

conditional control of process branch, generally used with elif and else.

x=int(input('请输入一个数字：'))
while x>0:
    print('正数')
    break

3.

for statement

Loop control statement can be used to traverse a certain object and is used together with in. Format: 【 for in

x=int(input('请输入一个数字：'))
if x<0:
    print(&#39;负数&#39;)
elif x==0:
    print(&#39;零&#39;)
else :
    print(&#39;正数&#39;)

4.

range

()

Function

Number sequence iterator, when you iterate over it, it is an object that can return consecutive items like the expected sequence, but to save space, it does not actually construct the list. Format: range(stop) gives the end value, the start value defaults to 0, and the interval is 1. Range (Start, Stop) gives the start value and end value, and the interval is 1.

Range (Start, STOP, STEP) gives the start value and end value, and the interval is STEP value.

x=['a','b','c','d']for i in x :  
            # i 位置的字符，只要不是关键字，可以随意用字符代表
    print(i)

class range(object):
    """
    range(stop) -> range object
    range(start, stop[, step]) -> range object
    
    Return an object that produces a sequence of integers from start (inclusive)
    to stop (exclusive) by step.  range(i, j) produces i, i+1, i+2, ..., j-1.
    start defaults to 0, and stop is omitted!  range(4) produces 0, 1, 2, 3.
    These are exactly the valid indices for a list of 4 elements.
    When step is given, it specifies the increment (or decrement).
    """
    def count(self, value): # real signature unknown; restored from doc
        """ rangeobject.count(value) -> integer -- return number of occurrences of value """
        return 0

    def index(self, value, start=None, stop=None): # real signature unknown; restored from doc
        """
        rangeobject.index(value, [start, [stop]]) -> integer -- return index of value.
        Raise ValueError if the value is not present.
        """
        return 0

    def contains(self, *args, **kwargs): # real signature unknown
        """ Return key in self. """
        pass

    def eq(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def getattribute(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def getitem(self, *args, **kwargs): # real signature unknown
        """ Return self[key]. """
        pass

    def ge(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def gt(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    def hash(self, *args, **kwargs): # real signature unknown
        """ Return hash(self). """
        pass

    def init(self, stop): # real signature unknown; restored from doc
        pass

    def iter(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def len(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def le(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def lt(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @staticmethod # known case of new
    def new(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def ne(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def reduce(self, *args, **kwargs): # real signature unknown
        pass

    def repr(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def reversed(self, *args, **kwargs): # real signature unknown
        """ Return a reverse iterator. """
        pass

    start = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    step = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    stop = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

5.break and

continue

statements, and the else statement in the loop

1) break The statement is similar to the one in C

, used to jump out of the nearest level for or while loop.

for i in range(3):          #运行结果为0，1，2
    print(i)
for i in range(0,5):       #运行结果为0，1，2，3，4
    print(i)
for i in range(-2,10,2): #运行结果为-2，0，2，4，6，8
    print(i)

2) continue

statement

indicates that the loop continues to execute the next iteration

:

while True:
    print('hello')
    break

3) else in the loop

For example, in the continue example, there are for-else statements and else statements It will be executed after the loop jumps out, but break will not execute else when it jumps out of the loop, so else can be used to handle some exceptions in the loop.

for x in range(1, 4):
        print(x, 'for语句')
        continue
        print(x, 'continue语句后')
else:
        print(x, 'else语句')
 
#运行结果
for语句
for语句
for语句
else语句

6.pass statement

The pass statement does nothing. It is used in situations where syntactically necessary statements are required, but the program does nothing. It is usually used to create minimally structured classes.

On the other hand, pass can be used as a placeholder for a function or control body when creating new code. Allows you to think on a more abstract level.

for x in range(1, 4):
        print(x)
else:
        print(x)

#运行结果
2
3

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