第2章 Python 必须知道的基础语法

本章知识

1、Python 文件的扩展名；
2、Python 的编码规则；
3、数据类型；
4、变量和常量的定义和使用；
5、运算符及表达式；

内容

2.1 Python 的文件类型
    2.1.1 源代码
    2.1.2 字节代码
    2.1.3 优化代码
        （1）、启动命令行窗口；
        （2）、在命令行中输入 python-O-m py_compile hello.py;
2.2 Python的编码规范
    2.2.1 命名规则
        （1）、变量名、包名、模块名；
        （2）、类名、对象名；
            class Student:
                __name = ""
                def __init__(self, name):
                    self.__name = name
                def getName(self):
                    return self.__name
            if __name__ == "__main__":
                student = Student("borphi")
                print(student.getName())
            #  输出：borphi
        （3）、函数名；
            import random
            def compareNanum(num1, num2):
                if (num1 > num2):
                    return 1
                elif(num1 == num2):
                    return 0
                else:
                    return -1
            num1 = random.randrange(1, 9)
            num2 = random.randrange(1, 9)
            print ("num1 =", num1 )
            print ("num2 =", num2)
            print (compareNanum(num1, num2))
            #  输出：num1 = 5; num2 = 3; 1
        # 不规范的命名
        sum = 0
        i = 2000
        j = 1200
        sum = i + 12 * j
        print (sum)
        #输出：16400

        #规范的命名
        sumPay = 0
        bonusOfYeay = 2000
        monthPay = 1200
        sumPay = bonusOfYeay + 12 * monthPay
        print (sumPay)
        #输出：16400
    2.2.2 代码缩进与冒号
        x = 1
        if x == 1:
            print ("x =", x)
        else:
            print ("x =", x)
            x = x + 1
        print ("x =", x)
        输出：x=1 x=1
        x = 2
        if x == 1:
            print ("x =", x)
        else:
            print ("x =", x)
            x = x + 1
        print ("x =", x)
        输出：x=2 x=3
        x = 1
        if x == 1:
            print ("x =", x)
        else:
            print ("x =", x)
        x = x + 1
        print ("x =", x)
        # 输出: x=1; x=2
    2.2.3 模块导入的规范
        （1）、import 语句
            import sys
            print (sys.path)
            print (sys.argv)
            输出：['D:\\Python\\零基础学 python\\第2章 Python 必须知道的基础语法',
                'D:\\Python\\零基础学 python', 'F:\\Anaconda3\\python36.zip',
                'F:\\Anaconda3\\DLLs', 'F:\\Anaconda3\\lib', 'F:\\Anaconda3',
                'F:\\Anaconda3\\lib\\site-packages',
                'F:\\Anaconda3\\lib\\site-packages\\win32',
                'F:\\Anaconda3\\lib\\site-packages\\win32\\lib',
                'F:\\Anaconda3\\lib\\site-packages\\Pythonwin',
                'C:\\PyCharm 2017.3.3\\helpers\\pycharm_matplotlib_backend']
                ['D:/Python/零基础学 python/第2章 Python 必须知道的基础语法/hello.py']
        （2）、from...import... 语句
            from sys import path
            from sys import argv
            print (path)
            print (argv)
            输出：['D:\\Python\\零基础学 python\\第2章 Python 必须知道的基础语法',
                'D:\\Python\\零基础学 python', 'F:\\Anaconda3\\python36.zip',
                'F:\\Anaconda3\\DLLs', 'F:\\Anaconda3\\lib', 'F:\\Anaconda3',
                'F:\\Anaconda3\\lib\\site-packages',
                'F:\\Anaconda3\\lib\\site-packages\\win32',
                'F:\\Anaconda3\\lib\\site-packages\\win32\\lib',
                'F:\\Anaconda3\\lib\\site-packages\\Pythonwin',
                'C:\\PyCharm 2017.3.3\\helpers\\pycharm_matplotlib_backend']
                ['D:/Python/零基础学 python/第2章 Python 必须知道的基础语法/hello.py']
    2.2.4 使用空行分割代码
        class A:
            def funX(self):
                print ("funY")

            def funY(self):
                print ("funX")

        if __name__ == "__main__":
            a = A()
            a.funX()
            a.funY()
        # 输出：funX; funY
    2.2.5 正确的注释
        （1）、中文注解
            # -*- coding:utf-8 -*-
        （2）、跨平台注解
            # !/usr/bin/python
            def compareNum(num1, num2):
                if (num1 > num2):
                    return str(num1)+">"+str(num2)
                elif(num1 < num2):
                    return str(num1)+"<"+str(num2)
                elif(num1 == num2):
                    return str(num1)+"="+str(num2)
                else:
                    return ""
            num1 = 2
            num2 = 1
            print (compareNum(num1, num2))
            num1 = 2
            num2 = 2
            print (compareNum(num1, num2))
            num1 = 1
            num2 = 2
            print (compareNum(num1, num2))
            # 输出：2>1;2=2;1<2

2.2.6 语句的分割
        print ("hello world!")
        print ("hello world!");

        x = 1;y = 2; z = 3;
        print (x, y, z)
        # 输出：hello world!  hello world!  1 2 3
2.3 变量和常量
    2.3.1 变量的命名
        var_1 = 1
        print (var_1)
        _var1 = 2
        print (_var1)
        # 输出：1； 2
    2.3.2 变量的赋值
        x = 1
        print (id(x))
        x = 2
        print (id(x))
        # 输出：1611623488; 1611623520
        a = (1,2,3)
        (x, y, z) = a
        print ("x =", x)
        print ("y =", y)
        print ("z =", z)
        # 输出：x = 1; y = 2; z = 3
    2.3.3 局部变量
        def fun():
            local = 1
            print (local)
        fun()
        # 输出：1
    2.3.4 全局变量
        _a = 1_b = 2
        def add():
            global _a
            _a = 3
            return "_a + _b =", _a+_b  # _a=3;_b=2
        def sub():
            global _b
            _b = 4
            return "_a - _b =", _a-_b  #_a=3;_b=4
        print (add())
        print (sub())
        # 输出：('_a + _b =', 5)； ('_a - _b =', -1)
        _a = 1
        _b = 2
        def add():
            _a = 3
            return "_a + _b =", _a+_b  # _a=3;_b=2
        def sub():
            _b = 4
            return "_a - _b =", _a-_b  #_a=1;_b=4
        print (add())
        print (sub())
        # 输出：('_a + _b =', 5)； ('_a - _b =', -3)

    2.3.5 常量
        class _const:
            class ConstError(TypeError):
                pass
            def __setattr__(self, name, value):
                if self.__dict__.has_key(name):
                    raise self.ConstError,  "Can't rebind const(%s)" %name
                self.__dict__[name] = value
        import sys
        sys.modules[__name__] = _const()
        # 输出：SyntaxError: invalid syntax
        import const
        const.magic = 23
        const.magic = 33
2.4 数据类型
    2.4.1 数字
        i = 1
        print (id(i))
        i = 2
        print (id(i))
        i = 1
        print (type(i))
        i = 999999999999990
        print (type(1))
        f = 1.2
        print (type(f))
        b = True
        print (type(b))
        # 输出：1611623488； 1611623520； <class 'int'>； <class 'int'>；
               <class 'float'>； <class 'bool'>

    2.4.2 字符串
        str = "hello world!"
        print (str)
        str = 'hello world!'
        print (str)
        str = '''he say "hello world!"'''
        print (str)
        # 输出：hello world!
               hello world!
               he say "hello world!"
        class Hello:
            '''hello class'''
            def printHello():
                '''print hello world'''
                print ("hello world")
        print (Hello.__doc__)
        print (Hello.printHello.__doc__)
        # 输出：hello class
        #      print hello world
        str = '''he say: 'hello world!' '''
        print (str)
        str = 'he say :\'hello world!\''
        print (str)
        str = "he say: 'hello world!'"
        print (str)
        # 输出：he say: 'hello world!'
        #      he say :'hello world!'
        #      he say: 'hello world!'
2.5 运算符与表达式
    2.5.1 算术运算符和算术表达式
    print ("1 + 1 =", 1+1)
    print ("2 - 1 =", 2-1)
    print ("2 * 3 =", 2*3)
    print ("4 / 2 =", 4/2)
    print ("1 / 2 =", 1/2)
    print ("1.0 / 2.0 =", 1.0/2.0)
    print ("3 % 2 =", 3%2)
    print ("2 ** 3 =", 2**3)
    # 输出：1 + 1 = 2
    #      2 - 1 = 1
    #      2 * 3 = 6
    #      4 / 2 = 2.0
    #      1 / 2 = 0.5
    #      1.0 / 2.0 = 0.5
    #      3 % 2 = 1
    #      2 ** 3 = 8
    a = 1
    b = 2
    c = 3
    d = 4
    print ("a + b * c % d =", a+b*c%d)
    print ("(a + b) * (c % d)=", (a+b)*(c%d))
    # 输出：a + b * c % d = 3
    #      (a + b) * (c % d)= 9
    2.5.2 关系运算符和关系表达式
        print (2 > 1)
        print (1 <= 2)
        print (1 == 2)
        print (1 != 2)
        # 输出：True
        #      True
        #      False
        #      True
        print ("1 + 2 < 3 - 1 =>", 1 + 2, "<", 3 -1, "=>", 1 + 2 < 3 - 1 )
        print ("1 + 2 <= 3 > 5 % 2 =>", 1 + 2, ">", 5 % 2, "=>", 1 + 2 <= 3 > 5 % 2)
        # 输出：1 + 2 < 3 - 1 => 3 < 2 => False
        #      1 + 2 <= 3 > 5 % 2 => 3 > 1 => True
    2.5.3 逻辑运算符和逻辑表达式
        print (not True)
        print (False and True)
        print (True and False)
        print (True or False)
        # 输出：False
        #      False
        #      False
        #      True
        print ("not 1 and 0 =>", not 1 and 0)
        print ("not (1 and 0) =>",not (1 and 0))
        print ("(1 <= 2) and False or True =>", (1 <= 2) and False or True)
        print ("(1 <= 2) or 1 > + 2 =>", 1 <= 2, "or", 1 > 2, "=>", (1 <= 2) or (1 < 2))
        # 输出：not 1 and 0 => False
        #      not (1 and 0) => True
        #      (1 <= 2) and False or True => True
        #      (1 <= 2) or 1 > + 2 => True or False => True