Python 基础语法复习

因为选修了《人工智能模式识别》的课程，要求用phthon来实现算法，乘着周三晚上没课，就来回顾一下python的主要语法。

环境：   Anaconda

　　　   Python3.6

1.变量：

• 在python中，变量是不须要提早声明类型的

1 #data type 2 str_test = "China" 3 int_test = 123 4 float_test = 122.5 5 6 print(str_test) 7 print(int_test) 8 print(float_test) 

• 类型能够转换，用type查看变量类型

 1 #转换  2 str_eight = str(8)  3 eight = 8  4 str_eight_two = str(eight)  5  6 str_eight = "8"  7 int_eight = int(str_eight)  8  9 print(int_eight) 10 print(type(int_eight))

2.list类型

• list类型里的元素类型能够不一样，添加元素时可用list.apppend(),添加时自动为其设置下标index,可以使用下标访问list中的元素

 1 countries = [] 2 temperatures = [] 3 4 countries.append("China") 5 countries.append("India") 6 countries.append("United States") 7 8 temperatures.append(30.5) 9 temperatures.append(25.0) 10 temperatures.append(15.1) 11 12 print(countries) 13 print(temperatures) 14 15 china = countries[0] 16 china_temperature = temperatures[0] 17 print(china) 18 print(china_temperature)

• 计算list长度，切片操做，值得注意的是list[-1] == list[length-1], 即下标是循环的

 1 int_months = [1,2,3,4,5,6,7,8,9,10,11,12] 2 length = len(int_months) 3 print(length) 4 index = len(int_months)-1 5 last_value = int_months[index] 6 print(last_value) 7 print(int_months[-1]) #倒数也可 8 #切片 9 two_four = int_months[2:4] #取头不取尾 10 print(two_four) 11 tree_last = int_months[3:] 12 print(tree_last)

 

3.程序的结构

• loop>>for,  range()的用法值得注意

1 #loop 2 cities = ["Austin","Dallas","Houston"] 3 for city in cities: 4 print(city) 5 for i in range(10): 6 print(i)

• loop>>while

1 i = 0 2 while i < 3: 3 i += 1 4 print(i)

• 双重循环

1 cities = [["Austin","Dallas","Houton"],["Haerbin","Shanghai","Beijing"]] 2 print(cities) 3 #for city in cities: 4 #print(city) 5 6 for i in cities: 7 for j in i: 8 print(j)

• 判断语句

1 #if statements 2 sample_rate = 700 3 greater = (sample_rate > 5) 4 if greater: #也能够为表达式 5 print(sample_rate) 6 else: #不写else也能够 7 print('less than')

• list中查找的简写

1 #find a value  2 animals = ["cat","dog","rabbit"] 3 for animal in animals: 4 if animal == "cat": 5 print("Cat found") 6 if "cat" in animals: 7 print("2 is also right")

4.dictionary类型

• 字典的建立、初始化和赋值

 1 students = {} 2 students["Tom"] = 60 3 students["Jim"] = 70 4 print(students) 5 6 students = {} 7 students = { 8 "Tom": 60, 9 "Jim": 70 10 } 11 print(students)

 

• 字典的应用----统计个数

 1 #统计  2 pantry = ["apple", "orange", "grape", "apple", "orange", "apple", "tomato", "potato", "grape"]  3 pantry_counts = {}  4  5 for item in pantry:  6 if item in pantry_counts:  7 pantry_counts[item] = pantry_counts[item] + 1  8 else:  9 pantry_counts[item] = 1 10 print(pantry_counts)

5.文件处理

• 文件的读与写

1 f = open("test_write.txt","w") #不存在的文件自动新建 2 f.write("123456") 3 f.write("\n") 4 f.write("234567") 5 6 f.close()

 1 #File 2 #打开 3 f = open("test.txt","r") 4 5 #处理 6 g = f.read() 7 print(g,type(g)) 8 9 #关闭 10 f.close() #不要忘了关闭

 

• 文件csv的操做举例以及split()的使用

 1 weather_data = [] 2 f = open("weather.csv",'r') 3 data = f.read() 4 #print(data) 5 rows = data.split("\n") 6 #print(rows) 7 for row in rows: 8 split_row = row.split(",") 9 print(split_row) 10 weather_data.append(split_row[0]) 11 print(weather_data) 12 f.close()

操做该部分时，我先创建了一个xlsx文件，随后将名称改成了csv文件，打不开文件，使用“rb”操做后显示乱码。随后发现另存为csv文件能够很好的解决这个问题，对csv文件的构成也有了深入的了解。

6.函数的操做

1 def printHello(): 2     print("hello python") 3     
 4 def printNum(): 5     for i in range(0,10): 6         print(i) 7     return
 8 def add(a,b): 9     return a+b 10 printHello() 11 printNum() 12 add(1,2)

与C/C++不一样，传入参数不须要申明类型。