Python[十七]:Iterator

#Python Iterator#iteratorfor element in[1,2,3]: print(element)for element in (1,2,3): print(element)for key in {'One':1,'Two':2}: print(key)for char in "123": print(char)#for line in open('class2.py'):# print(line)#show what happend for'next()'s='abc'it=iter(s)print(it)print(next(it))print(next(it))#print(next(it))#print(next(it))#create our own __iter__()and __next__() funcclass Reverse: """iterator for looping over a sequense backwards""" def __init__(self,data): self.data=data self.index=len(data) def __iter__(self): return self def __next__(self): if self.index==0: raise StopIteration self.index=self.index-1 return self.data[self.index]for char in Reverse('spam'): print(char,end=' ')print()#generators#Each time next() is called on it, the generator resumes where it left-off#(it remembers all the data values and which statement was last executed).def reverse(data): for index in range(len(data)-1,-1,-1): yield data[index]for char in reverse('golf'): print(char,end=' ')print()#Generator Expressionsprint(sum(i*i for i in range(10))) #sum of squaresxvec=[10,20,30]yvec=[7,5,3]print(sum(x*y for x,y in zip(xvec,yvec))) ##dot productfrom math import pi,sin#sine tablesine_table={x:sin(x*pi/180) for x in range(0,91)}print(sine_table,end=' ')print()#unipue words#------unique_words=set(word for line in page for word in line.split())#------valedictorian=max((student.gpamstudent.name) for student in graduates)data='golf'print(list(data[i] for i in range(len(data)-1,-1,-1)))