Python 编程

标签：case linlee name Point Python 编程 print

第1章什么是 Python?

  # Python——编程新手最好的选择

第2章为 Python 做好准备

  # 单行注释 打印出单词 "Hello World"
  print("Hello World")
  ''' 多行注释
      这是一条注释
      这也是一条注释
  '''
  print("Hello Python")

第3章变量和操作符的世界

3.1 定义变量

  userAge, userName = 16, 'saber'
  """
  <==>
  userAge = 16, userName = 'saber'
  <==>
  userAge = 16
  userName = 'saber'
  """

3.2 命名变量

  与 C 一致:
    1. 字母数字下划线;
    2. 不能为关键字;
    3. 区分大小写;
  命名规则举例:
    1. 驼峰式: ThisIsAVariableName
    2. 下划线式: this_is_a_variable_name

3.3 赋值符号

  x = 8
  y = 2
  x = y
  print("x =",x)  # x = 2
  print("y =",y)  # y = 2

3.4 基本操作符

+	-	*	/	//	%	**
加法	减法	乘法	除法	整除	取余	指数

  x = 5
  y = 2
  print("x+y =",x+y)  # x+y = 7
  print("x-y =",x-y)  # x-y = 3
  print("x*y =",x*y)  # x*y = 10
  print("x/y =",x/y)  # x/y = 2.5
  print("x//y =",x//y)  # 向下取整 x//y = 2
  print("x%y =",x%y)  # x%y = 1
  print("x**y =",x**y)  # x**y = 25
  print('100 + 200 =', 100 + 200, 1-2, 10/3, 10//3, 10%3, 2*3, 2**10)

3.5 更多的分配操作符

+= -= *=

第4章 Pyhon 中的数据类型

4.1 整数类型 int

  print(123_456_578, 0x1011_0010, 0xFFBC_9890, -9, 0)

4.2 浮点类型 float

  print(-18.579, 1.974e6, 1.4e-8, 124.089_743_572_903_8)

4.3 字符串 str

  userName = 'peter', userSpouseName = "Janet", usrAge = '30'
  # 字符串中使用 "" 或 '' 都可以,但必须配对使用,不能 ' " 单独使用
  # 可以使用 + 连接多个字符串
  print("I love"+" Saber"+" forever!")  # "I love Saber forever!"
  print('alice', "I'm Bob.", '\t hello, Eve', 'How are you? I\'m fine, thanks!', '\\\n\\\\%', r'\\\n\\\\t\\\b\\', '''
  line1,
  line2,
  line3''', "'Hello, world'", "'hello,\\\'Adam\\\''", "r\'hello,\"Bart\"\'")

4.3.1 内建的字符串函数

  'excalibur'.upper() # 将字符串中每一个字符都转化为大写

4.3.2 使用 % 操作符格式化字符串

  # 格式化输出
  age = 12
  location = 'Xi\'an, Shaanxi'
  price = 9.962
  rate = 0.23528
  print('I\'m %d years old, and I come from %s. The price of the book is $%.2f, its increase rate is %.1f %%' % (age, location, price, rate*100) )
  # I'm 12 years old, and I come from Xi'an, Shaanxi. The price of the book is $9.96, its increase rate is 23.5 %
  # 引号内编写要格式化的字符串，写出% 使用一对小括号，括号内写上要插入字符串的值或变量
  # 这对包含值的小括号事实上叫做——元组 %d %f %s 宽度，保留小数位数等与 C 一致
  brand = 'Apple'
  exchangeRate = 1.235235344 
  message = 'The price of this %s laptop is %d USD and the exchange rate is %4.2f USD to 1 EUR' %(brand, 1299, exchangeRate)
  print(message) # The price of this Apple laptop is 1299 USD and the exchange rate is 1.24 USD to 1 EUR

4.3.3 使用 format() 方法格式化字符串

  message = 'The price of this {0:s} laptop is {1:d} USD and the exchange rate is {2:4.2f} USD to 1 EUR'.format("Apple", 1299, 1.4354351)
  print(message)  # The price of this Apple laptop is 1299 USD and the exchange rate is 1.44 USD to 1 EUR
  message = 'The price of this {} laptop is {} USD and the exchange rate is {} USD to 1 EUR'.format("Apple", 1299, 1.4354351)
  print(message)  # The price of this Apple laptop is 1299 USD and the exchange rate is 1.4354351 USD to 1 EUR
  message1 = '{0} is easier than {1}'.format("Python",'Java')
  message2 = '{1} is easier than {0}'.format("Python","Java")
  message3 = '{:10.2f} and {:d}'.format(1.23454545,12)
  message4 = '{}'.format(1.233455644)
  print(message1) # Python is easier than Java
  print(message2) # Java is easier than Python
  print(message3) #       1.23 and 12
  print(message4) # 1.233455644

4.4 Python 中的类型转换

  # Python中的三个内建函数 int()   float()   str()
  print(int(2.34))  # 2
  print(int("4654"))  # 4654
  print(int(8)+6)  # 14
  print(float(6+7))  # 13.0
  print(float("85438.443"))  # 85438.443
  print(float("5"))  # 5.0
  print(str(6))  # 6
  print(str(9.56)+"dfjgh")  # 9.56dfjgh
  print(str("534fdf"))  # 534fdf

4.5 列表 list

  # list
  # a. 使用中括号[]
  # b. 索引从0开始，最后一个元素为-1，倒数第二为-2 依此类推
  # c. 1:5叫做切片，它总是包括开始索引的元素，而不包括结尾索引的元素 1:5表示从索引1到索引4 = 5-1
  # d. 切片第三个数字叫做步长 [1:5:2]从索引位置1~4=5-1 中每隔一个数字的子列表，故步长为2 
  # e. 若不指定则默认:第一个数字为0，第二个数字为列表长度  [:4]表示0~3   [2:]表示2~4 总长为5，共有5个元素
  linlee = ['Michael', 123, 'Bob', [99.98, '$'], 'Tracy', True]
  print(linlee, len(linlee), type(linlee) )
  print(linlee[-1], linlee[0], linlee[1], linlee[3], len(linlee[3]), linlee[3][1])
  linlee.append('Adam')   # 追加元素到列表末尾
  print(linlee)
  linlee.insert(1,'Jack') # 插入元素到列表指定位置
  print(linlee)
  linlee.pop()    # 删除列表末尾元素
  print(linlee)
  linlee.pop(1)   # 删除列表第二个元素
  print(linlee)
  linlee[1] = 'Sarah' # 修改列表中指定元素
  print(linlee)

4.6 元组 tuple

  # tuple 不可变更的 list
  month = ("Jan","Feb","Mar")
  classmates = ('Alice', 99.9, 'Bob', False, 'Eve', 0)
  print(classmates, len(classmates), type(classmates))
  t1 = () # 空 tuple
  t2 = (1,)   # 仅有一个元素 1 的 tuple
  t3 = (1)    # <==> t3 = 1 不是 tuple
  print(t1, t2, t3, type(t1), type(t2), type(t3), len(t1), len(t2))
  # "可变的" tuple
  t4 = ('a', 'b', ['A', 'B'])
  print(t4)
  t4[2][0] = 'X'
  print(t4)
  # 检索
  name = (
      ('Apple', 'Google', 'Microsoft'),
      ('Java', 'Python', 'Ruby', 'PHP'),
      ('Adam', 'Bart', 'Lisa')
  )
  print(name[0][0])
  print(name[1][1])
  print(name[2][2])

4.7 字典 dict

list	dict
查找插入时间随元素增加而增加	查找插入快，与元素多少无关
内存占用小	内存占用多
元素可以重复	key 不允许重复

  userNameAndAge = {"peter":34,"John":42,"Saber":16,"Archer":"Not Available"}
  userNameAndAge = dict(peter=34,John=42,Saber=16,Archer="Not Available")
  # dict
  name_to_score = {'Alice':95, 'Bob':99, 'Eve':92}
  print(name_to_score['Bob'])
  print('Thomas' in name_to_score) # 检查 'Thomas' 是否存在
  print(name_to_score.get('Thomas'))  # 检查 'Thomas' 是否存在, 不存在时返回 None
  name_to_score.pop('Bob')    # 删除 key

4.8 集合 set

  # set
  s1 = set([1, 2, 3, 3, 2, 1])
  s2 = set([3, 4, 5, 1, 1])
  s1.add(4)
  s2.remove(4)
  print(s1)
  print(s2)
  print (s1 & s2)
  print (s1 | s2)
  s3 = set((1, 2, 3))
  s3.add(4)
  s3.remove(3)
  print(s3)
  s4 =set(1, [2, 3])  # TypeError: set expected at most 1 argument, got 2
  print(s4)
  s4 =set(1, 2, 3)  # TypeError: set expected at most 1 argument, got 3
  print(s4)
  s4 = set((1, [2, 3]))   # TypeError: unhashable type: 'list'
  print(s4)
  s4 = set((1, (2, 3)))
  print(s4)

第5章程序可交互

5.1&5.2 input() print()

  myName = input("Please enter your name: ")
  myAge = input("What about your age: ")
  print("Hello World,my name is ",myName,"and I am",myAge,"years old.")

5.3 三引号

  print('''Hello World.
  My name is John and
  I am 20 years old.''')

5.4 转义字符
```
  print("a\tb\nc\\d\"e\'f")
```

第6章选择和判断

6.1 条件语句

==	!=	<	>	<=	>=	and	or	not
等于	不等于	小于	大于	小于等于	大于等于	与	或	非

6.2 if

  user = input("Enter 1 or 2:")
  if user == "1":
      print("Hello World")
      print("How are you")
  elif user == "2":
      print("Python Rocks")
      print("Ilove Python")
  else:
      print("You didn't enter a valid number!")
  # if elif else
  height = float(input('Please input your height(m): '))
  weight = float(input('Please input your weight(kg): '))
  bmi = weight / (height * height)
  print('Your bmi is %.2f.' % bmi)
  if bmi < 18.5 :
      print('too light.')
  elif bmi < 25 :
      print('normal.')
  elif bmi < 28 :
      print('overweight.')
  elif bmi < 32 :
      print('obese.')
  else :
      print('too obese.')
  # inline if
  user = input("Enter 1 or 2:")
  num=1 if user=="1" else 5
  print(num)
  print("This is task A " if user=="2" else "This is task B")

6.3 match case

  # match
  # basic match
  score = 'B'
  match score:
      case 'A':
          print('score is A.')
      case 'B':
          print('score is B.')
      case 'C':
          print('score is C.')
      case _: # _表示匹配到其他任何情况
          print('score is ?.')
  # sequence match
  point = (2, 7)
  match point:
      case (0, 0):
          print('Origin')
      case (0, y):
          print(f'Point is on the Y axis at {y}')
      case (x, 0):
          print(f'Point is on the Y axis at {x}')
      case (x, y):
          print(f'Point is at ({x}, {y})')
      case _:
          print('Not a point')
  # object match
  class Point:
      def __init__(self, x, y):
          self.x = x
          self.y = y
  p = Point(0, 3)
  match p:
      case Point(x=0, y=0):
          print(f'Point is on origin')
      case Point(x=0, y=y):
          print(f'Point is on the Y axis at {y}')
      case Point(x=x, y=0):
          print(f'Point is on the X axis at {x}')
      case Point(x=x, y=y):
          print(f'Point is at ({x}, {y})')
      case _:
          print('Not a point')
  # band match
  x = 2
  match x:
      case x if x > 3:
          print(f'{x} > 3')
      case 1 | 2 | 3:
          print("x is 1, 2, or 3")
      case _:
          print("x is something else")
  # list match
  args = ['gcc', 'hello.c', 'world.c']
  # args = ['clean']
  # args = ['gcc']
  match args:
      case ['gcc']:   # 列表仅有'gcc'一个字符串，没有指定文件名，报错
          print('gcc: missing source code file(s).')
      case ['gcc', file1, *files]:    # 列表第一个字符串是'gcc'，第二个字符串绑定到变量file1，后面的任意个字符串绑定到*files
          print('gcc compile: ' + file1 + ',' + ','.join(files))
      case ['clean']: # 列表仅有'clean'一个字符串
          print('clean')
      case _: # 其他所有情况
          print('invalid command.')

6.4 for 循环

6.4.1 迭代

  pets = ["cats","dogs","rabbits","hamsters"]
  for mypets in pets:
      print(mypets)
  for index, mypets in enumerate(pets):
      print(index, mypets)
  message = "Hello"
  for i in message:
      print(i)

6.4.2 在一段数字上循环 range(start, end, step), 默认 start == 0, step == 1 生成连续列表 end 必须显式给出

  range(5) # 生成[0,1,2,3,4]     
  range(3,10) # 生成[3,4,5,6,7,8,9]     
  range(4,10,2) # 生成[4,6,8]
  for i in range(5):
      print(i)

6.5 while 循环

  counter = 5
  while counter>0:
      print("counter = ",counter)
      counter = counter - 1

6.6 break

j = 0
for i in range(5):
    j=j+2
    print("i=",i,"j=",j)
    if(j==6):
        break

6.7 continue

j = 0
for i in range(5):
    j=j+2
    print("i=",i,"j=",j)
    if(j==6):
        continue
    print("if counter!=6,print counter=",i)

6.8 Try, Except

[格式] try子句（可能出错的语句） except子句（错误发生，执行的语句）

  def spam(divideBy):
      try:
          return 42/divideBy
      except ZeroDivisionError:
          print('Error:Invalid argument')
  print(spam(2))
  print(spam(12))
  print(spam(0))
  print(spam(3))

  None 的输出是因为 print()函数的返回值为 none

标签：case,linlee,name,Point,Python,编程,print
From： https://www.cnblogs.com/Avalon-Nausica/p/18166629

第1章什么是 Python?

第2章为 Python 做好准备

第3章变量和操作符的世界

第4章 Pyhon 中的数据类型

第5章程序可交互

第6章选择和判断

相关文章

赞助商

阅读排行

Python 编程

第1章 什么是 Python?

第2章 为 Python 做好准备

第3章 变量和操作符的世界

第4章 Pyhon 中的数据类型

第5章 程序可交互

第6章 选择和判断

相关文章

赞助商

阅读排行

第1章什么是 Python?

第2章为 Python 做好准备

第3章变量和操作符的世界

第5章程序可交互

第6章选择和判断