1 python基础

一、变量和list

1、定义一个变量，并赋值。

days_1 = 365
days_2 = 366

#修改变量值
number_of_days = 365
print(number_of_days)   # 365
number_of_days = 366
print(number_of_days)  # 366

#打印
#print
print(365)       # 365
print("hello")   # hello

• 1.1 数值型变量有float和integer两种
• 1.2 非数值型变量通常为string

str_test = "China"
int_test = 123
float_test = 122.5

print(str_test)  # China

print(int_test)  # 123

print(float_test) # 122.5

print(type(str_test))     # <class 'str'>
print(type(int_test))     # <class 'int'>
print(type(float_test))  # <class 'float'>

2、类型转换函数

　　str()    、  float()     、 int()

查看变量的数据类型，函数：type()

str_eight = str(8)
#str_eight + 10  # 异常：TypeError: can only concatenate str (not "int") to str
print(type(str_eight))        # <class 'str'>
print(type(float(str_eight))) # <class 'float'>
print(type(int(str_eight)))   # <class 'int'>
print(str_eight + 'a')        # 8a

print('---------')

eight = 8
str_eight_two = str(eight)
print(type(eight))           # <class 'int'>
print(type(str_eight_two))   # <class 'str'>

二、注释

单行注释、多行注释

#单行注释
#print test


# 多行注释
"""
Addition:+
Subtraction:-
Multiplication:*
Division:/
Exponent:**
"""

三、数值运算

china=10
united_states=100
china_plus_10 = china + 10
us_times_100 = united_states * 100
print(china_plus_10)
print(us_times_100)
print(china**2)  # 平方**

四、list类型变量

1、定义一个list类型变量

#LIST
months = []
print(type(months))  # <class 'list'>
print(months)        # []

months.append("January")
months.append("February")
print(months)        # ['January', 'February']

# 定义一个list，然后进行赋值
months = []
months.append(1)
months.append("January")
months.append(2)
months.append("February")
print(months)        # [1, 'January', 2, 'February']

#定义并初始化list变量
temps = ["China",122.5,"India",124.0,"United States",134.1]
print(type(temps))  # <class 'list'>
print(temps)        # ['China', 122.5, 'India', 124.0, 'United States', 134.1]
# 获取list的某一elem元素
print(temps[1])     # 122.5
print(temps[2])     # India

2、长度函数: len()

int_months = [1,2,3,4,5,6,7,8,9,10,11,12]
lenght = len(int_months) #Contains the integer value 12
print(lenght)    # 12

int_months = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
index = len(int_months) - 1     # 11
# 通过索引寻址
last_value = int_months[index]  # 12
print(last_value)               # 12
# 通过-1索引寻找队列最后一个值
print(int_months[-1])           # 12

3、list切片，分段，子集

有头无尾：指定开始索引，不指定结束索引

# 切片
months = ["Jan","Feb","Mar","Apr","May","Jun","Jul"]
#指定起止索引。Values at index 2,3, but not 4.  前闭后开区间
two_four = months[2:4]
print(two_four)      # ['Mar', 'Apr']


# 指定开始索引，不指定结束索引
three_six = months[3:]
print(three_six)        # ['Apr', 'May', 'Jun', 'Jul']

无头有尾：不指定开始位置，指定结束位置

# 不指定开始位置，指定结束位置
f = open('dq_unisex_names.csv','r')  # open()函数操作文件
names = f.read()                     # 读取文件内容
names_list = names.split('
')       # 将文件内容按换行符切分得到一个names_list
first_five = names_list[:5]  # 等于names_list[0:5]
print(first_five)  # ['Casey,176544.3281', 'Riley,154860.6652', 'Jessie,136381.8307', 'Jackie,132928.7887', 'Avery,121797.4195']

转换为二维列表

# 转换为二维列表
f = open('dq_unisex_names.csv', 'r')
names = f.read()
names_list = names.split('
')
nested_list = []
for line in names_list:
    comma_list = line.split(',')
    nested_list.append(comma_list)
print(nested_list[0:5])    #  [['Casey', '176544.3281'], ['Riley', '154860.6652'], ['Jessie', '136381.8307'], ['Jackie', '132928.7887'], ['Avery', '121797.4195']]

将数值转换为float类型，遍历实现

nested_list = [['Casey', '176544.3281'], ['Riley', '154860.6652'], ['Jessie', '136381.8307'], ['Jackie', '132928.7887'], ['Avery', '121797.4195']]
numerical_list = []
for line in nested_list:
    name = line[0]    # line是一个list
    count = float(line[1])
    num_list = [name, count]
    numerical_list.append(num_list)
    
print(numerical_list)  # [['Casey', 176544.3281], ['Riley', 154860.6652], ['Jessie', 136381.8307], ['Jackie', 132928.7887], ['Avery', 121797.4195]]

list函数，append() 将子元素添加到list

从文件中读取不同日期的天气数据到list列表

# 从文件中读取不同日期的天气数据到list列表

weather_data = []
f = open("la_weather.csv",'r')
data = f.read()
rows = data.split('
')
# print(rows)
for row in rows:
    split_row = row.split(',')
    weather_data.append(split_row)
print(weather_data)  # [['1', 'Sunny'], ['2', 'Sunny'], ['3', 'Sunny'], ['4', 'Sunny'], ['5', 'Sunny'], ['6', 'Rain'], ['7', 'Sunny'], ['8', 'Sunny'], ['9', 'Fog'], ['10', 'Rain']]

读出天气数据到weather列表

# 读出天气数据到weather列表
weather = []
for row in weather_data:
    weather.append(row[1])
print(weather) # ['Sunny', 'Sunny', 'Sunny', 'Sunny', 'Sunny', 'Rain', 'Sunny', 'Sunny', 'Fog', 'Rain']
f.close()

判断list中是否包含'cat' ： 'cat'   in   xx

# 列表中寻找值
animals = ['cat','dog','rabbit']
for animal in animals:
    if animal == 'cat':
        print('Cat found')
      
# in 语句，判断是否在列表  
cat_found = 'cat' in animals
print(cat_found)

4、读取文件，切分str得到list

4.1 文件操作函数：open("file","op")

# 读文件
f = open("test.txt","r")

g = f.read()
print(g)

f.close()

# 写文件
f = open("test_write.txt","w")

f.write("123456")
f.write("
")
f.write("234567")

f.close()

# 切分string得到list.
str_ex = "john,plastic,joe"
split_list = str_ex.split(',')
print(split_list)        # ['john', 'plastic', 'joe']

string_two = "How much wood
can a woodchuck chuck
if a woodchuck
could chuck wood?"
list_2 = string_two.split('
')
print(string_two)
print(list_2) # ['How much wood', 'can a woodchuck chuck', 'if a woodchuck', 'could chuck wood?']

4.2 读文件内容，得到string，split()函数切分string得到list

# 读文件内容，得到string，split()函数切分string得到list
f = open('test.txt','r')
data = f.read()
rows = data.split('
')
print(rows)  # ['hello python', 'tangyudi 123', 'ML 456', 'DL 789', 'data 234']

4.3 遍历 list  ：  for  in

# loop LIST:  for  in
cities = ["Austin", "Dallas", "Houston"]
for city in cities:
    print(city)
print("123")

Austin
Dallas
Houston
123

4.4 遍历list： while

# loop  define:  while
cities = ["Austin", "Dallas", "Houston"]
i = 0
while i < len(cities):
    print(cities[i])
    i += 1
    

Austin
Dallas
Houston

 4.5 range(n)   、  range(start,end,step)

rg = range(15)
print(rg)
for i in rg:
    print(i)
    

# 设置起止和步长
rg2 = range(0,20,5)
print(rg2)
for i in rg2:
    print(i)

4.6 嵌套list的遍历

cities = [["Austin","Dallas","Houston"],['Haerbin','Shanghai','Beijing']]
print(cities)
for lst in cities:
    for city in lst:
        print(city)

[['Austin', 'Dallas', 'Houston'], ['Haerbin', 'Shanghai', 'Beijing']]
Austin
Dallas
Houston
Haerbin
Shanghai
Beijing

五、布尔类型

# Booleans
cat = True
dog = False
print(type(cat))   # <class 'bool'>
print(dog)         # False

print(8 == 8) # True
print(8 != 8) # False
print(8 == 10) # False
print(8 != 10) # True

print("abc" == 'abc') # True
print(["January","February"] == ["January","February"]) # True
print(5.0 == 5.0) # True

true等于1，false等于0

rates = [10, 15, 20]

print(rates[0] > rates[1]) # False
print(rates[0] >= rates[0]) # True
print(False == 0)  # True
print(True == 1)   # True
print(True == 3)   # False
print(True == 'a') # False

在 if 语句中，非0都为true

# If Statements
sample_rate = 700
greater = (sample_rate > 5)
if 'a':  # if条件中，值非0则为True
    print(sample_rate)
else:
    print("less then")

700

t = True
f = '棒'

if t:
    print("Now you see me")

if f: 
    print("Now you don't")

Now you see me
Now you don't

六、dict 字典类型

用于存储键值对，比如，学生成绩。

定义一个字典，变量={ }。赋值新增一个元素，变量['元素名']=值。

scores = {}  #定义一个scores字典
print(type(scores))     # <class 'dict'>
scores["Jim"] = 80      # 新增“Jim”的成绩80
scores["Sue"] = 85
scores["Ann"] = 75
print(scores.keys())    # dict_keys(['Jim', 'Sue', 'Ann'])   获取字典的所有key
print(scores.values())  # dict_values([80, 85, 75])          获取字典的所有value
print(scores)           # {'Jim': 80, 'Sue': 85, 'Ann': 75}
print(scores["Sue"])    # 85

# 初始化
# 方式1
students = {}
students["Tom"] = 60
students["Jim"] = 70
print(students)   # {'Tom': 60, 'Jim': 70}

# 方式2
students = {"Tom":60, "Jim":70}
print(students)   # {'Tom': 60, 'Jim': 70}

字典对象的增删改查

# 增删改查
students = {
    "Tom": 60,
    "Jim": 70
}
# 增
students["Ketty"] = 80
print(students)  # 查

# 改
students["Tom"] = 65
print(students['Tom']) # 查
students['Tom'] += 5   # 改
print(students)        # 查 {'Tom': 70, 'Jim': 70, 'Ketty': 80}
# 更新 update
students.update({"mogen":77, "Tom":60})  # 新增mogen，修改Tom
print(students)        #  {'Tom': 60, 'Jim': 70, 'Ketty': 80, 'mogen': 77}

# 删
del students['Tom']    # 删
print(students)        # {'Jim': 70, 'Ketty': 80, 'mogen': 77}
# 清空
students.clear()
print(students)        # {}

判断字典是否包含对象： in语句# 遍历，字典

# 判断字典中是否包含对象
students = {
    "Tom": 60,
    "Jim": 70
}
print("mogen" in students)  # False
print('Jim' in students)    # True


# 遍历
# 统计单词出现次数
pantry = ["apple", "orange", "grape", "apple", "orange", "apple", "tomato", "potato", "grape"]
pantry_counts = {}

for item in pantry:
    if item in pantry_counts:
        pantry_counts[item] += 1
    else:
        pantry_counts[item] = 1
print(pantry_counts)   # {'apple': 3, 'orange': 2, 'grape': 2, 'tomato': 1, 'potato': 1}

 七、函数

定义一个函数：无参数，无返回值

 函数
# 无参数，无返回值
def firFun():
    print("hello python")

无参数，有返回None

# 无参数，有返回None
def numFun():
    for i in range(0, 10):
        i
    return

有参数，有返回值

# 有参数，有返回值
def add(a, b):
    return a+b

---------------------------

print(firFun())

hello python
None

print(numFun())   # None
print(add(3, 5))  # 8