python基础--异常，对象和迭代器

Posted 2020-09-18

• 异常处理
• 面向对象
• 迭代器和生成器

python异常处理

• 下面代码触发了一个FileNotFoundError

>>> open("notexist.txt")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: ‘notexist.txt‘

• 抛出异常

>>> raise FileNotFoundError

• 异常类型

• 捕获异常使用try,except,finally,else

try:
  open(r"c:\\Users\\kingsoft\\Desktop\\notexist.txt")
except FileNotFoundError as e:
  print ("file not exist...")
except (name1,name2):
  print ("io error is true...")
else:
  print ("file exist..")
finally:
  print ("always do...")

　　

python面向对象

python是完全面向对象的，python中一切都是对象，包括变量，函数等。

• 定义一个对象

class MyException():
	pass

• self 和init方法

class Person():

	def __init__(self, name):
		self.name = name	
	
	def sayname(self):
		print self.name

m = Person("joe")
print(m.sayname())

• 区分类和类的实例

class Person():
	def __init__(self, name):
		self.name = name	
		Person.name = name
	def sayname(self):
		print("myname is :" + self.name)
		print("myexceptionname is: " + Person.name)
	def changeothername(self, name):
		Person.name = name
	def __del__(self):
		print(self.name + "is gone")
m = Person("joe")
m.sayname()
print("m.name : " + m.name)
m.test="tt"
print(m.test)
j = Person("jason")
j.sayname()
j.changeothername(j.name)
m.sayname()

• 类的继承，多态和封装概念

生成器和迭代器

• _iter_方法返回迭代器，迭代器指有next方法的对象

class Fibs(object):
	"""docstring for Fibs"""
	def __init__(self, max):
		self.max = max
		self.a = 0
		self.b = 1
	def __next__(self):
		fib = self.a
		if fib > self.max:
			raise StopIteration
		self.a, self.b = self.b, self.a + self.b
		return fib
	#返回迭代器
	def __iter__(self):
		return self
fib = Fibs(1000)
for f in fib:
	print(f, end= " ")

• 可迭代对象Iterable和迭代器Iterator
• 生成器，生成器通过yield语句快速生成迭代器，让函数变成一个生成器

#斐波那契数列
def getfibs(max):
	a = 0
	b = 1
	while a < max:
		a, b= b, a+b
		value = a
		yield value

print(getfibs(1000))
for i in getfibs(1000):
	print(i)

• 简单理解生成器

def gen():
	yield "hello"
	yield "how"
	yield "are"
	yield "you"
for i in gen():
	print(i)