Python operators and control flow

Operators in Python

What are operators? Take a simple example 4 +5 = 9. In the example, 4 and 5 are called operands, and "+" is called the operator.

1. Exponentiation operator

In Java, if we want to exponentiate a number, we may have to resort to pow() in the Math library function, but in Python we can use two consecutive * to represent the exponentiation operation.

a = 5 ** 2
print a

2 . // Operator

Many people may want to say, I know this, I type Comments often use double slashes, but it is very embarrassing. The single-line comment symbol in Python is #, and multi-line comments can use '''. So what is // used for? Used to find the integer part of dividing two numbers.

a = 10.0 // 3
print a

At this time, 3.0 will be output, which is the integer part of the division, and the remainder will be ignored.

3. &, | Operator

Everyone knows these two operators, & bitwise AND, | bitwise OR, let’s talk about these two operators The operating principle of each operator. How much does a number 7&18 equal? ​​Try running it in the compiler

a = 7 & 18
print a

The printed result is 2. why? It's very simple. We first need to convert 7 and 18 into binary, 7-> 00000111 18->00010010, and then perform an AND operation on these two binary numbers. What is the AND operation? Just remember that when the two numbers are both 1 in the same position, the result is 1, and the other numbers are 0. The operation process is as follows

It is obvious that the result is 2. The | operator is the same as the & operation steps. However, during the | operation process, as long as the two numbers are at the same position, If one is 1, then the result is 1. You can calculate it yourself, so I won’t go into details here.

4 . >>,

When I first saw this symbol, my first reaction was that it is far greater than and far Far less than, does this mean right shift and left shift, left shift and right shift? How to move? Similarly, you need to convert the decimal number into binary form, and then shift left and right. In fact, shifting left once is equivalent to multiplying a number by 2, shifting left n times is multiplying a number by 2 n times, and shifting right Instead, it is divided by 2 raised to the 'n' power.

# coding=utf-8

# 左移2位
a = 5 << 2
print a

# 右移三位
b = 32 >> 3
print b

5 . not, and, or operators

These three are logical operators, in other If you want to express OR and NOT in a programming language, you might use the format ||,&&,!, but in Python you need to use or,and,not.

a = True
b = False

c = not a
d = a and b
e = a or b

print c
print d
print e

The results are False False True

6. We will not introduce the operators, but let’s take a look at the precedence of the operators. , I made a picture

The closer to the fish head, the higher the level.

Python control flow

The so-called control flow is nothing more than if..else, while, for, etc. Everyone knows the basic usage, but Python always has its special features. Let’s take a look.

1 . if...else

if judgment statement has a place worth introducing, as shown below

a = 10
if 5 <= a <= 10:
  print a

In Java language, you probably have to write like this

int a = 10;
if(a >= 5 && a <= 10){
  System.out.println(a);
}

2 . while , for

The only thing you need to remember is that in Python, whether it is for or while, you can add an else statement at the end like if. The else statement will be executed after the loop statement jumps out.

a = False
while a:
  print ("I am while")
else:
  print ("I am else")

for i in range(1, 2):
  print ("I am for")
else:
  print ("I am else")

Tips: range() The function can set the step interval, what does it mean? Try it yourself~

Summary

The above is all about operators and control flow in Python, what this article talks about It is basic introductory knowledge, but it is also a very important part. I hope it will be helpful to everyone in using Python.

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