1.运算符的优先级
print(3*1**3) #3 相当于：3*(1**3)
2.小整数池
a = 1
b = 1
print(a is b) # True
a = 300
b = 300
print(a is b) # True
# 在shell里是False
# [-5, 256]之间的整数，值相同的整数共享一个对象
# is 比较内存地址
# == 比较对象的值
3.字符串
def foo1(a):
a = a +"2"
a = a * 2
return a
print(foo1("hello")) # hello2hello2
# 操作符重载
# __add__(+)
# __mul__(*)
#例如：
class Point(object):
def __init__(self, x, y):
self.x = x
self.y = y
def __add__(self, other):
return Point(self.x + other.x, self.y + other.y)
def __mul__(self, other):
return Point(self.x * other.x, self.y * other.y)
def __repr__(self):
return "Point({}, {})".format(self.x, self.y)
p1=Point(1,2)
p2=Point(3,4)
print(p1+p2) # Point(4, 6)
print(p1*p2) # Point(3, 8)
4.浮点数
print(0.3) # 0.3
print(0.1 + 0.2) # 0.30000000000000004
print(0.1 + 0.2 == 0.3) # False
5.取反操作
print(~5) # -6
print(~~5) # 5
print(~~~5) # -6
# ~按位取反，计算机以补码存储
6.布尔
print(bool("Flase")) # True
7.链式比较
print(True == False ) # False
print(False ==False) # True
print(True == False ==False) # False
# 相当于 (True == False) and (False == False)
8.循环语句
i = 0
while i < 5:
print(i)
i += 1
if i ==3:
break
else:
print(0)
"""
0
1
2
"""
9.作用域
x = 12
def f1():
x = 3
print(x)
def f2():
global x # 没有这个声明报错，local variable 'x' referenced before assignment
x += 1
print(x)
f1()
f2()
10.python关键字
eval("1-1") # eval不是关键字，是内建函数
assert(1 == 1)
pass
# nonlocal
import keyword
print(keyword.kwlist)
"""33
['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class',
'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for',
'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal',
'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
"""
