Basic knowledge of Python

The overall introduction is here

1. Variable Definition

You needn't assign a type to a variable, because Python interpreter will automatically judge the type. You needn't declare a variable before define. The following is an example of how to state a variable:
python 复制代码
a = 1

b = "hello"

c = 3.14159
As you can see, definition of variable is simple, just use = .

The name of variable shoule make up letters, $, numbers, and _ . A variable mustn't begin with a number.

Note that in the instance above, a,b and c is the reference of the variable. That is, 1 "hello" and 3.14159 is in the heap memory and a,b and c just their alias. It is important.

2. Comment

Comment is important for us to understand the function of our code. We use # to indicate the line is a comment.
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# This is a comment
# The comment will be ignored by the interpreter.

a = 1 # You can also add a comment here, too.
b = "hello"
c = 3.14159

3. Type of variable

We needn't declare the type of a variable, but it doesn't mean that a variable hasn't a type.

There are many types in Python:

|----------|-----------------------------------------------------------|-------------|
| int | integer | a = 10 |
| float | folat number | a = 1.2 |
| complex | complex number | a = 1 + 2j |
| bool | True or False | a = False |
| str | a string of charactors | a = "hello" |
| Sequence | a special type of variable which we will explore it later | |
| None | indicates that a variable is empty | a = None |

When you define a variable, the interpreter will judge the type of the variable automatically.

4. build-in functions

We haven't explore what is function now, so if you can't understand what functions are, you can just memorize the form and use it. You will definitely understand it later.

|---------|---------------------------------------------------------------------------------------------------------------|--------------------------|
| print() | a powerful function which can print out content to your terminal, which can receive almost any type of input. | print(1) |
| | | print("hello") |
| | | print(...) |
| len() | It will return the "length" of an object. The "length" is defined by the object. We will talk about it later. | len([1,2,1]) #return 3 |