How do I know if a generator is empty from the start?

Suggestion:

def peek(iterable):    try:        first = next(iterable)    except StopIteration:        return None    return first, itertools.chain([first], iterable)

Usage:

res = peek(mysequence)if res is None:    # sequence is empty.  Do stuff.else:    first, mysequence = res    # Do something with first, maybe?    # Then iterate over the sequence:    for element in mysequence:        # etc.

The simple answer to your question: no, there is no simple way. There are a whole lot of work-arounds.

There really shouldn't be a simple way, because of what generators are: a way to output a sequence of values without holding the sequence in memory. So there's no backward traversal.

You could write a has_next function or maybe even slap it on to a generator as a method with a fancy decorator if you wanted to.

A simple way is to use the optional parameter for next() which is used if the generator is exhausted (or empty). For example:

iterable = some_generator()_exhausted = object()if next(iterable, _exhausted) == _exhausted:    print('generator is empty')

Edit: Corrected the problem pointed out in mehtunguh's comment.