python之数值类型

数值numbers

数值类型分为int类型和float类型#和其他程序设计语言一样

python中+，-，*，/的使用同其他程序设计语言也一样，遵循先乘除后加减，括号内先执行，略微不同的是/,稍后有介绍

>>> 2 + 2
4
>>> 50 - 5*6
20
>>> (50 - 5*6) / 4
5.0
//the operators +, -, * and / work just like in most other languages (for example, Pascal or C);

>>> 17 / 3  # classic division returns a float
5.666666666666667
//此处‘/’默认返回的是浮点数类型（相比c语言中的'/'，都是整数默认返回整数，类似求整操作，而python中返回float，取整操作为‘//’）
>>>
>>> 17 // 3  # floor division discards the fractional part
5//python中的取整操作
>>> 17 % 3  # the % operator returns the remainder of the division
2 //返回余数
>>> 5 * 3 + 2  # result * divisor + remainder
17

#x**y等于power（x,y）
>>> 5 ** 2  # 5 squared
25
//5的平方
>>> 2 ** 7  # 2 to the power of 7
128
//2的7次方

>>> width = 20
>>>width
20
>>> height = 5 * 9
>>>height
45
>>> width * height
900
//‘=’等号用以给变量赋值

>>> n  # try to access an undefined variable
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'n' is not defined
//如果没有事前定义变量，直接使用会出错

>>> tax = 12.5 / 100
>>> price = 100.50
>>> price * tax
12.5625
>>> price + _
113.0625
//此处_值为上一步price * tax的值12.5625
>>> round(_, 2)
113.06
//此处_值为上一步打印出来的113.0625，操作保留2位小数

布尔类型Booleans

t = True
f = False
print(type(t)) # Prints "<class 'bool'>"
print(t and f) # Logical AND; prints "False"
print(t or f) # Logical OR; prints "True"
print(not t) # Logical NOT; prints "False"
print(t != f) # Logical XOR; prints "True"

字符串string类型

hello = 'hello' # String literals can use single quotes
world = "world" # or double quotes; it does not matter.
print(hello) # Prints "hello"
print(len(hello)) # String length; prints "5"
hw = hello + ' ' + world # String concatenation
print(hw) # prints "hello world"
hw12 = '%s %s %d' % (hello, world, 12) # sprintf style string formatting
print(hw12) # prints "hello world 12"

s = "hello"
print(s.capitalize()) # Capitalize a string; prints "Hello"
print(s.upper()) # Convert a string to uppercase; prints "HELLO"
print(s.rjust(7)) # Right-justify a string, padding with spaces;
print(s.center(7)) # Center a string, padding with spaces; 
print(s.replace('l', '(ell)')) 
# Replace all instances of one substring with another substring
 # prints "he(ell)(ell)o"
print(' world '.strip()) # Strip leading and trailing whitespace;