如何判断Python中zip()函数生成的对象是否为空？

Great question! Since zip() in Python 3 returns an iterator (not a list or other sequence), you can’t directly use len() to check if it’s empty—iterators don’t store their full length in memory. Here are reliable, practical methods to determine if a zip object is empty, along with how to apply them to your code:

Method 1: Efficient Check with next() (Preserves the Iterator) #

This approach only checks the first element of the iterator, making it memory-efficient even for large datasets. If you need to use the iterator after checking, we can "restore" the first element we pulled out.

import itertools

# Your original data
transactions = ['001','002','003']
transaction_dates = ['01-01-2019','01-02-2019','01-03-2019']
transaction_amounts = ['27.00','35.00','36.00']

results = zip(transactions, transaction_dates, transaction_amounts)

is_empty = False
try:
    # Try to get the first element of the zip iterator
    first_item = next(results)
    # Restore the iterator by chaining the first element back in
    results = itertools.chain([first_item], results)
except StopIteration:
    # If StopIteration is raised, the iterator is empty
    is_empty = True

print(f"Is results empty? {is_empty}")  # Output: Is results empty? False

Method 2: Simple Check by Converting to a List (Consumes the Iterator) #

If you don’t need to reuse the original zip iterator, converting it to a list is the easiest way. Just check if the resulting list is empty:

results = zip(transactions, transaction_dates, transaction_amounts)
results_list = list(results)

if not results_list:
    print("Zip object is empty")
else:
    print(f"Zip object has {len(results_list)} items")
    # Use results_list for further processing (original iterator is now exhausted)

Note: This works well for small datasets, but for very large iterables, converting to a list will use more memory.

Method 3: Reusable Helper Function #

For repeated use, wrap the check in a helper function that returns both the empty status and the restored iterator (if not empty):

import itertools

def is_iterator_empty(iterator):
    try:
        first_element = next(iterator)
        return False, itertools.chain([first_element], iterator)
    except StopIteration:
        return True, iterator

# Usage with your data
results = zip(transactions, transaction_dates, transaction_amounts)
empty_status, results = is_iterator_empty(results)

print(f"Empty? {empty_status}")

Key Notes #

• zip() returns an empty iterator if any of the input iterables is empty (since it stops at the shortest input).
• In Python 2, zip() returns a list instead of an iterator, so len(zip(...)) would work directly—but this is irrelevant for modern Python versions.

内容的提问来源于stack exchange，提问作者Reez0