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Python学习笔记一:数据类型与基本操作

2015-06-23 10:27 986 查看
Python学习笔记一:数据类型与基本操作

一、Python字符串

1.1 可以在三种引号内表示字符串

'This is a string'

"This is a string"

"""This is a string"""

1.2 使用print函数

print("Hello World! ")

Hello World! 

1.3 转义字符\后的特殊字符会被看成字符

>>> print("I said, \"Don't do it")

I said, "Don't do it

1.4 可是使用三引号分行打印,使用单引号或双引号则不行

>>> print("""Rose are red

... Violets are blue

... I just printed multiple lines

... And you did too!""")

Rose are red

Violets are blue

I just printed multiple lines

And you did too!

1.5 使用双引号与换行转义字符实现分行打印

>>> print("Roses are red \n Violets are blue \n I just printed multiple lines \n And you did too!")

Roses are red 

Violets are blue 

I just printed multiple lines 

And you did too!

1.6 连接字符串

>>> "John" + "Everyman"

'JohnEveryman'

>>> "John" "Everyman"

'JohnEveryman'

1.7 使用格式说明符%s连接字符串

>>> "John Q. %s" % ("Public")

'John Q. Public'

>>> "John %s%s" % ("Every","man")

'John Everyman'

1.8 %s连接字符串并限定长度

>>> "%-10s %s %10s" % ("John","Every","Man")

'John       Every        Man'

第一个字符串在右边填充6个字符,第三个字符串在左右填充7个字符。

1.9 将其他类型转化为字符串

>>> "This is a string" + str(4)

'This is a string4'

二、Python数值与计算

2.1 使用type函数查看数值类型

>>> type(1)

<type 'int'>

>>> type(1.1)

<type 'float'>

2.2 数字格式说明符

>>> "Including an integer works with %%d like this : %d" % 10

'Including an integer works with %d like this : 10'

>>> "An integer converted to a float with %%f: %f" % 5

'An integer converted to a float with %f: 5.000000'

>>> "A normal float with %%f: %f" % 1.2345

'A normal float with %f: 1.234500'

>>> "A really large number with %%E: %E" % 6.789E10

'A really large number with %E: 6.789000E+10'

>>> "Controlling the number of decimal places shown: %.02f" % 25.101010101

'Controlling the number of decimal places shown: 25.10'

最后一个例子表示四舍五入到小数点后面两位。

2.3 除法与取余运算

>>> 6 / 4

1

>>> 6 % 4

2

2.4 除法结果处理实例

>>> print("%f" % (5/3))

1.000000

>>> print("%.2f" % (5/3))

1.00

>>> print("%.2f" % (415 * 20.2))

8383.00

>>> print("%0.f" % (415 * 20.2))

8383

2.5 真除法与取底除法

>>> from __future__ import division

>>> 10/4

2.5

>>> 10//4

2

2.5 二进制、八进制与十六进制

2.5.1 表示方法


>>> abin=0b0011

>>> abin

3

>>> aoct=0o12

>>> aoct

10

>>> ahex=0xE

>>> ahex

14

2.5.2 格式说明符

>>> print('Octal uses the letter "o" lowercase. %d %o' % (10,10))

Octal uses the letter "o" lowercase. 10 12

>>> print('Hex uses the letter "x" or "X". %d %x %X' % (10,10,10))

Hex uses the letter "x" or "X". 10 a A

2.6 转换函数

>>> oct(64),hex(64),bin(64)

('0100', '0x40', '0b1000000')

>>> int(0x40),float(0b1000000)

(64, 64.0)

三、变量、元组、列表及字典

3.1 变量名称只是实际对象的一个指针

>>> a=1

>>> b=a

>>> print(a)

1

>>> print(b)

1

>>> a=a+1

>>> print(a)

2

>>> print(b)

1

3.2 元组——不可更改的数据序列

3.2.1 创建和使用元组


>>> a = ("string","filled","by a","tuple")

>>> print(a)

('string', 'filled', 'by a', 'tuple')

3.2.2 元组的索引(从0开始)及长度

>>> a = ("first", "second", "third")

>>> print("The first element of the tuple is %s" % a[0])

The first element of the tuple is first

>>> print("%d" % len(a))

3

3.2.3 嵌套元组及索引

>>> a = ("first", "second", "third")

>>> b = (a, "b's second element")

>>> print ("%s" %b[1])

b's second element

>>> print("%s" % b[0][0])

first

>>> print("%s" % b[0][1])

second

>>> print("%s" % b[0][2])

3.2.4 创建一个元素的元组(必须加",")

>>> single_element_tuple = ("the sole element",)

3.2 列表——可更改的数据序列

3.2.1 创建使用列表


>>> breakfast = ["coffee", "tea", "toast" , "egg"]

>>> count = 0

>>> print("Today's breakfast is %s" % breakfast[count])

Today's breakfast is coffee

>>> count = 1

>>> print("Today's breakfast is %s" % breakfast[count])

Today's breakfast is tea

>>> count = 2 

>>> print("Today's breakfast is %s" % breakfast[count])

Today's breakfast is toast

>>> count = 3

>>> print("Today's breakfast is %s" % breakfast[count])

Today's breakfast is egg

3.2.2 添加一个元素

>>> breakfast = ["coffee", "tea", "toast" , "egg"]

>>> breakfast.append("waffles")

>>> count = 4

>>> print("Today's breakfast is %s" % breakfast[count])

Today's breakfast is waffles

3.2.3 为列表添加多个元素

>>> breakfast

['coffee', 'tea', 'toast', 'egg', 'waffles']

>>> breakfast.extend(["juice", "decaf", "oatmeal"])

>>> breakfast

['coffee', 'tea', 'toast', 'egg', 'waffles', 'juice', 'decaf', 'oatmeal']

3.3 字典——键值存储数据

3.3.1 创建与使用字典


>>> menus_specials = {}

>>> menus_specials["breakfast"] = "Canadian ham"

>>> menus_specials["lunch"] = "tuna surprise"

>>> menus_specials["dinner"] = "Cheesebruger Deluxe"

or

>>> menu_specials = {"breakfast" : "sausage and eggs",

... "lunch" : "split pea soup and garlic bread",

... "dinner" : "2 hot dogs and onion rings"}

>>> print(menu_specials["breakfast"])

sausage and eggs

3.3.2 获取字典的所有键以及所有值

>>> hungry = menu_specials.keys()

>>> print(hungry)

['lunch', 'breakfast', 'dinner']

>>> starving = menu_specials.values()

>>> print(starving)

['s
bba1
plit pea soup and garlic bread', 'sausage and eggs', '2 hot dogs and onion rings']

字典中键都是不同的,只能通过键找值,如果需要通过值找键,则需要测试所有键。

3.3.3 字典中定义相同的键,值将被覆盖

>>> menu2 = {"breakfast" : "spam", "breakfast" : "ham", "dinner" : "hotdog"}

>>> menu2.get("breakfast")

'ham'

3.3.4 其他类型

None:仅仅是一个名称,没有指向任何对象。

True False:1 0 的特殊表示。

3.4 序列(字符串、元组或列表)的共有属性

3.4.1 访问最后一个元素


sequence[len(sequence)-1]或者sequence[-1]

>>> sequence = (1,2,3,4,5)

>>> sequence[-1]

5

>>> sequence[-2]

4

3.4.2 序列分片

>>> s="abcde"

>>> s[-1]

'e'

>>> s[1:5]

'bcde'

>>> l = [0,1,2,3,4]

>>> l[1:3]

[1, 2]

3.4.3 append方法与extend方法

>>> t = ("a", "b", "c")

>>> l = []

>>> l.append(t)

>>> l

[('a', 'b', 'c')]

>>> t = ("a", "b", "c")

>>> l = []

>>> l.extend(t)

>>> l

['a', 'b', 'c']

3.4.4 列表的pop方法

>>> l = ["a", "b", "c", "d", "e"]

>>> l.pop()

'e'

>>> l

['a', 'b', 'c', 'd']

>>> l.pop(0)

'a'

>>> l

['b', 'c', 'd']

>>> l.pop(1)

'c'

>>> l

['b', 'd']

3.4.5 set方法删除列表的重复元素

>>> l

['a', 'b', 'c', 'b', 'c']

>>> l2 = list(set(l))

>>> l2

['a', 'c', 'b']
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