Python 3.x:测试生成器是否有剩余元素 [英] Python 3.x: Test if generator has elements remaining

问题描述

当我在 for 循环中使用生成器时，它似乎知道"，当没有更多元素产生时.现在，我必须使用没有 for 循环的生成器，并手动使用 next() 来获取下一个元素.我的问题是，我怎么知道是否没有更多元素?

我只知道:next() 引发异常(StopIteration)，如果什么都没有，那么对于这样一个简单的问题，BUT 是不是有点太重"了?难道没有has_next()之类的方法吗?

以下几行应该清楚我的意思:

#!/usr/bin/python3# 定义一些对象的列表bar = ['abc'，123，无，真，456.789]# 我们的原始生成器定义富(酒吧):对于 bar 中的 b:产量 b# 迭代，使用上面的生成器print('--- TEST A (for 循环) ---')对于 foo(bar) 中的 baz:打印(巴兹)打印()# 为变量分配一个新的迭代器foob​​ar = foo(bar)print('--- TEST B (try-except) ---')而真:尝试:打印(foobar.__next__())除了停止迭代:休息打印()# 为变量分配一个新的迭代器foob​​ar = foo(bar)# 显示生成器成员print('--- 生成器成员 ---')print(', '.join(dir(foobar)))

输出如下:

--- TEST A(for循环)---美国广播公司123没有任何真的456.789--- 测试 B (try-except) ---美国广播公司123没有任何真的456.789--- 发电机成员 ---__class__，__delattr__，__doc__，__eq__，__format__，__ge__，__getattribute__，__gt__，__hash__，__init__，__iter__，__le__，__lt__，__name__，__ne__，__new__，__next__，__reduce__，__reduce_ex__，​​__repr__，__setattr__，__subsizeof__，gi_code、gi_frame、gi_running、发送、抛出

感谢大家，祝您有美好的一天！:)

解决方案

您编写的两个语句以完全相同的方式处理查找生成器的末尾.for 循环只是调用 .next() 直到引发 StopIteration 异常然后终止.

http://docs.python.org/tutorial/classes.html#iteratorsp>

因此，我不认为等待 StopIteration 异常是处理问题的繁重"方式，而是生成器的设计使用方式.

When I use a generator in a for loop, it seems to "know", when there are no more elements yielded. Now, I have to use a generator WITHOUT a for loop, and use next() by hand, to get the next element. My problem is, how do I know, if there are no more elements?

I know only: next() raises an exception (StopIteration), if there is nothing left, BUT isn't an exception a little bit too "heavy" for such a simple problem? Isn't there a method like has_next() or so?

The following lines should make clear, what I mean:

#!/usr/bin/python3

# define a list of some objects
bar = ['abc', 123, None, True, 456.789]

# our primitive generator
def foo(bar):
    for b in bar:
        yield b

# iterate, using the generator above
print('--- TEST A (for loop) ---')
for baz in foo(bar):
    print(baz)
print()

# assign a new iterator to a variable
foobar = foo(bar)

print('--- TEST B (try-except) ---')
while True:
    try:
        print(foobar.__next__())
    except StopIteration:
        break
print()

# assign a new iterator to a variable
foobar = foo(bar)

# display generator members
print('--- GENERATOR MEMBERS ---')
print(', '.join(dir(foobar)))

The output is as follows:

--- TEST A (for loop) ---
abc
123
None
True
456.789

--- TEST B (try-except) ---
abc
123
None
True
456.789

--- GENERATOR MEMBERS ---
__class__, __delattr__, __doc__, __eq__, __format__, __ge__, __getattribute__, __gt__, __hash__, __init__, __iter__, __le__, __lt__, __name__, __ne__, __new__, __next__, __reduce__, __reduce_ex__, __repr__, __setattr__, __sizeof__, __str__, __subclasshook__, close, gi_code, gi_frame, gi_running, send, throw

Thanks to everybody, and have a nice day! :)

解决方案

The two statements you wrote deal with finding the end of the generator in exactly the same way. The for-loop simply calls .next() until the StopIteration exception is raised and then it terminates.

http://docs.python.org/tutorial/classes.html#iterators

As such I don't think waiting for the StopIteration exception is a 'heavy' way to deal with the problem, it's the way that generators are designed to be used.

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