Python入门系列（三）基础数据类型

数据类型

您可以使用type（）函数获取任何对象的数据类型。

x = 5
print(type(x))

数字类型

x = 1    # int
y = 2.8  # float
z = 1j   # complex

Int，或integer，是一个长度不限的整数，正数或负数，不带小数。

x = 1
y = 35656222554887711
z = -3255522

浮点数，或“浮点数”是一个包含一个或多个小数的正数或负数。

x = 1.10
y = 1.0
z = -35.59

浮点数也可以是科学数字，用“e”表示10的幂。

x = 35e3
y = 12E4
z = -87.7e100

复数是用“j”作为虚部写成的

x = 3+5j
y = 5j
z = -5j

您可以使用int（）、float（）和complex（）方法从一种类型转换为另一种类型

x = 1    # int
y = 2.8  # float
z = 1j   # complex

#convert from int to float:
a = float(x)

#convert from float to int:
b = int(y)

#convert from int to complex:
c = complex(x)

Python没有生成随机数的random（）函数，但Python有一个内置的模块，名为random，可用于生成随机数

import random

print(random.randrange(1, 10))

字符串

可以使用三个引号将多行字符串指定给变量

a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."""
print(a)

要获得字符串的长度，请使用len（）函数。

a = "Hello, World!"
print(len(a))

要检查字符串中是否存在某个短语或字符，可以在中使用关键字in或者not in

txt = "The best things in life are free!"
print("free" in txt)

txt = "The best things in life are free!"
print("expensive" not in txt)

upper（）方法以大写形式返回字符串

a = "Hello, World!"
print(a.upper())

lower（）方法以小写形式返回字符串

a = "Hello, World!"
print(a.lower())

strip（）方法从开头或结尾删除任何空格

a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"

replace（）方法将一个字符串替换为另一个字符串

a = "Hello, World!"
print(a.replace("H", "J"))

split（）方法返回一个列表，其中指定分隔符之间的文本成为列表项。

a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']

要连接或组合两个字符串，可以使用+运算符。

a = "Hello"
b = "World"
c = a + b
print(c)

format（）方法接受传递的参数，对其进行格式化，并将其放置在占位符｛｝所在的字符串中

age = 36
txt = "My name is John, and I am {}"
print(txt.format(age))

format（）方法接受无限数量的参数，并放置在相应的占位符中：

quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))

您可以使用索引号｛0｝，以确保参数放置在正确的占位符中

quantity = 3
itemno = 567
price = 49.95
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))

要在字符串中插入非法字符，请使用转义字符。

txt = "We are the so-called "Vikings" from the north."

布尔值

除了空值（如（）、[]、｛｝、“、数字0和值None）之外，没有多少值的计算结果为False。当然，值False的计算结果为False。

# 下面将返回False
bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})

Python运算符

Python算术运算符

Operator	Name	Example
+	Addition	x + y
–	Subtraction	x – y
*	Multiplication	x * y
/	Division	x / y
%	Modulus	x % y
**	Exponentiation	x ** y
//	Floor division	x // y

赋值运算符

Operator	Example	Same As
=	x = 5	x = 5
+=	x += 3	x = x + 3
-=	x -= 3	x = x – 3
*=	x *= 3	x = x * 3
/=	x /= 3	x = x / 3
%=	x %= 3	x = x % 3
//=	x //= 3	x = x // 3
**=	x **= 3	x = x ** 3
&=	x &= 3	x = x & 3
\|=	x \|= 3	x = x \| 3
^=	x ^= 3	x = x ^ 3
>>=	x >>= 3	x = x >> 3
<<=	x <<= 3	x = x << 3

比较运算符

Operator	Name	Example
==	Equal	x == y
!=	Not equal	x != y
>	Greater than	x > y
<	Less than	x < y
>=	Greater than or equal to	x >= y
<=	Less than or equal to	x <= y

逻辑运算符

Operator	Description	Example
and	Returns True if both statements are true	x < 5 and x < 10
or	Returns True if one of the statements is true	x < 5 or x < 4
not	Reverse the result, returns False if the result is true	not(x < 5 and x < 10)

身份运算符

Operator	Description	Example
is	Returns True if both variables are the same object	x is y
is not	Returns True if both variables are not the same object	x is not y

成员运算符

Operator	Description	Example
in	Returns True if a sequence with the specified value is present in the object	x in y
not in	Returns True if a sequence with the specified value is not present in the object	x not in y

位运算符

Operator	Name	Description
&	AND	Sets each bit to 1 if both bits are 1
\|	OR	Sets each bit to 1 if one of two bits is 1
^	XOR	Sets each bit to 1 if only one of two bits is 1
~	NOT	Inverts all the bits
<<	Zero fill left shift	Shift left by pushing zeros in from the right and let the leftmost bits fall off
>>	Signed right shift	Shift right by pushing copies of the leftmost bit in from the left, and let the rightmost bits fall off