python入门基础语法

1、变量

变量类型：不用声明，赋值是什么类型该变量就是什么类型；

命名规则：全小写，使用下划线连接单词；

str_test = "China" int_test = 123 float_test = 123.5 print(str_test) print(type(str_test)) print(int_test) print(type(int_test)) print(float_test) print(type(float_test)) China <class 'str'> 123 <class 'int'> 123.5 <class 'float'>

2、类型转换

str_eight = str(8) int_eight = int(str_eight) print(type(str_eight)) print(type(int_eight)) <class 'str'> <class 'int'>

3、运算符

加 + 减 - 乘* 除/ 幂**，加减乘除大家都一样，就不多说了，幂：

int_days = 10 print(int_days ** 2) 100

4、List集合

声明、赋值和取值，下标index从0开始

months = [] months.append("January") months.append("February") print(months) print(months[0])

['January', 'February'] January int_months = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] #从后面开始取 print(int_months[-1]) #切片 取index为2和3的 不包含4 print(int_months[2:4]) #取index从5开始的到最后 print(int_months[5:]) #取index从0到2的 print(int_months[:3]) 12 [3, 4] [6, 7, 8, 9, 10, 11, 12] [1, 2, 3]

5、循环结构

通过冒号和缩进来控制代码块，类似Java的{}

citys = ["Beijing", "Shanghai", "Guangzhou"] for city in citys: print(city)

Beijing Shanghai Guangzhou

i = 0 while i < 3: i += 1 print(i)

1 2 3 for i in range(10): print(i) 0 1 2 3 4 5 6 7 8 9

6、判断结构

与其它语言没什么不同，没什么好讲的了。当直接使用数字时1=True，0=False

sample = 100 if sample > 1: print(sample) else: print("not found")

100 animals = ["cat", "dog", "rabbit"] if "cat" in animals: print("cat found") cat found

7、字典结构

即是key value 键值对

scores = {} scores["Jim"] = 80 scores["Sue"] = 85 scores["Ann"] = 75 print(type(scores)) print(scores) print(scores["Sue"])

<class 'dict'> {'Jim': 80, 'Sue': 85, 'Ann': 75} 85

students = { "Tom": 60, "Jim": 70 } print("Tom" in students)

True

8、文件操作

open(文件名,操作模式)  r为读，w为写，完成后记得close

f = open("d:\\test.txt", "w") f.write("123456") f.write("\n") f.write("234567") f.close() f = open("d:\\test.txt", "r") g = f.read() print(g) f.close()

123456 234567

读取一个csv文件放到List中，csv内容如下

weather_data = [] f = open("d:\\weather.csv", "r") data = f.read() rows = data.split('\n') for row in rows: split_row = row.split('\t') weather_data.append(split_row) print(weather_data) f.close()

[['1', 'Sunny'], ['2', 'Sunny'], ['3', 'Fog'], ['4', 'Rain'], ['5', 'Rain'], ['6', 'Sunny'], ['7', 'Fog']]

9、函数定义

def printHello(): print ('hello python') def add(a, b): return a + b printHello() print(add(1, 2))

hello python 3