Python 基础语法复习

由于选修了《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，变量是不需要提前声明类型的

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)

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)

• 类型可以转换，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))

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类型里的元素类型可以不同，添加元素时可用list.apppend(),添加时自动为其设置下标index,可使用下标访问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)

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，切片操作，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)

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)

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)

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)

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:        #也可以为表达式
5     print(sample_rate)
6 else:               #不写else也可以
7     print(less than)

1 #if statements 2 sample_rate = 700 3 greater = (sample_rate > 5) 4 if greater: #也可以为表达式 5 print(sample_rate) 6 else: #不写else也可以 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")

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

• 字典的创建、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)

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)

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("
")
4 f.write("234567")
5 
6 f.close()

1 f = open("test_write.txt","w") #不存在的文件自动新建 2 f.write("123456") 3 f.write(" ") 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

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的操作举例以及split()的使用

1 weather_data = []
 2 f = open("weather.csv",r)
 3 data = f.read()
 4 #print(data)
 5 rows = data.split("
")
 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()

1 weather_data = [] 2 f = open("weather.csv",r) 3 data = f.read() 4 #print(data) 5 rows = data.split(" ") 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()

操作该部分时，我先建立了一个xlsx文件，随后将名称改为了csv文件，打不开文件，使用“rb”操作后显示乱码。随后发现另存为csv文件可以很好的解决这个问题，对csv文件的构成也有了深刻的了解。

6.函数的操作

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)

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++不同，传入参数不需要申明类型。

由于选修了《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，变量是不需要提前声明类型的 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) 类型可以转换，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类型里的元素类型可以不同，添加元素时可用list.apppend(),添加时自动为其设置下标index,可使用下标访问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，切片操作，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: #也可以为表达式 5 print(sample_rate) 6 else: #不写else也可以 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 字典的创建、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(" ") 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的操作举例以及split()的使用 1 weather_data = [] 2 f = open("weather.csv",r) 3 data = f.read() 4 #print(data) 5 rows = data.split(" ") 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() 操作该部分时，我先建立了一个xlsx文件，随后将名称改为了csv文件，打不开文件，使用“rb”操作后显示乱码。随后发现另存为csv文件可以很好的解决这个问题，对csv文件的构成也有了深刻的了解。 6.函数的操作 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++不同，传入参数不需要申明类型。