Learn Python installation and basic grammar in one article - dry goods throughout

Install the Python program

Official website Python download address: Python Releases for Windows | Python.org

You can install version 3.7, and there may be minor changes in version upgrades. The following will be learned with python3.7 as an example

 

After downloading the installation package, double-click the brainless installation

Frequently asked questions for novices:

1. The symbols use Chinese characters

2. Code indentation

3. The built-in function in python is wrong

After the installation is complete, use the tools that come with python to learn programming

 

basic grammar learning

dir(__builtins__) #View built-in functions in python

>>> dir(__builtins__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'ModuleNotFoundError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError', 'RecursionError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopAsyncIteration', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '__build_class__', '__debug__', '__doc__', '__import__', '__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'breakpoint', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip']

1. Variables

name = '张三'

create variable procedure

Variable declaration first, variable assignment second

Variable name rules:

1. Variables are case-sensitive. If you use variables with different case, python will consider them as multiple variables.

2. It is not allowed to start with a number, not only python, but most languages ​​are not allowed

3. Do not start with a special symbol, you can start with an underscore _

define different statements

>>> name = '张三'
>>> print (name)
张三
>>> age = 17
>>> print (age)
17
>>> description="hello world!"
>>> print (description)
hello world!
>>> description_two="'hello world!'"
>>> print (description_two)
'hello world!'

2. escape

symbol	illustrate
\\	backslash (\)
\'	apostrophe(')
\"	Double quotes(")
\a	ring the bell
\b	backspace
\n	line break
\r	carriage return
\t	horizontal tab
\v	vertical tab
\f	Form feed
\ooo	ooo is octal
\xhh	hh is hexadecimal

3. Variables and strings

>>> print(520+1314)
1834
>>> print('520'+'1314')
5201314
>>> print(520+1314)
1834
>>> print('520'+'1314')
5201314

From this few lines of code, it can be seen that the sum of numbers is added when numbers are added, but the addition of strings is also called concatenation. Multiplication is used in strings to print multiple times, and strings can only be concatenated using the + symbol. Used with *, the string is the difference in type

4. Variable type escape

1.int()

You can convert numeric strings to int integers, but some letters or text will report an error

>>> age = '18'
>>> type (age)
<class 'str'>
>>> age_1 = int(age)
>>> type (age_1)
<class 'int'>

2.abs()

Convert numeric type to absolute value

>>> abs(-100)
100

3.float()

convert integer to float

>>> float(1)
1.0

4.bool()

>>> bool(100)
True
>>> bool(-1)
True
>>> bool(0)
False
>>> bool('false')
True
>>> bool(False)
False

5. Operators

arithmetic operator

operator	meaning
<	Determine whether the left side is smaller than the right side
<=	less than or equal to
>	more than the
>=	greater or equal to
==	Judging whether it is equal
！=	Is it not equal
is	Check if the ids of two objects are equal
is not	Determine if the ids of two objects are not equal

>>> 1 > 2
False
>>> 3 <= 5
True
>>> 3 == 3
True
>>> 3 != 3
False

Logical Operators

operator	meaning
and	Both left and right are true, the result is true
or	One of the left or right is true, the result is true
not	If true, the result is false, if false, the result is true

6. Loop structure

for loop

结构：
    for 变量 in 可迭代对象:
        statement()

Loop value:

>>> for i in "Curry":
    print (i)
C
u
r
r
y

range() iteration function

语法：
    range(stop)
    range(start,stop)
    range(start,start,step)

range usage:

>>> for i in range(5):
    print (i)
​
0
1
2
3
4
>>> for i in range(2,5):
    print(i)
​
2
3
4
>>> for i in range(1,5,2):
    print(i)
    
1
3
>>> for i in range(5,0,-1):
    print(i)
​
5
4
3
2
1

while loop

格式：
while 条件:
    条件为true的执行语句
    
第二种方式：
while 条件:
    代码块
else：
    当条件为假执行此代码块

Other loop items:

brack;      //结束当前循环
continue;   //跳出当前一层循环

7. Basic common modules

1.random random number module

>>> import random
>>> print (random.randint(1,10))
4

2.decimal precision floating point number module

>>> import decimal
>>> 0.1 + 0.2
0.30000000000000004
>>> a = decimal.Decimal('0.1')
>>> b = decimal.Decimal('0.2')
>>> print (a+b)
0.3

3.len() to get the length

>>> len('Curry')
5
>>> test=[1,2,3,4,5,'Curry']
>>> len(test)
6

8. Types in python

• floating point

• integer

• string

• plural

• Boolean

9. Business logic

flow chart

 

mind Mapping

10. The Great Judgment Branch

1. Single judgment

if 条件:
    代码块

2. Double branch judgment

if 条件:
    代码块
else:
    代码块

3. Multi-branch judgment

if 条件:
    代码块
else if:
    代码块
else if:
    代码块
else:
    代码块

4. Special way of writing judgment

格式：为true代码块 if 条件 else 为false结果
>>> if 0 < 1:
    print ("True")
else:
    print ("False")
​
True
>>> print ("True") if 0 < 1 else print ("False")
True