What does enumerate() mean?

Index offset with enumerate()

It is possible to tinker around with the starting point of our counter. The enumerate() function accepts a second parameter to set the starting index.

for i, v in enumerate(['a', 'b', 'c'], start=1):
    print(i, v)  # "I don't always start counting at zero. But when I do ..."
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Starting from another number can be beneficial when working with 1-indexed data or to match human numbering conventions.

Enumerate() in versatile scenarios

Hop, skip, and loop

While traversing a list, there may be times when we might want to hop over certain rows. How do we skip over these gracefully? Introducing 'enumerate()', your loop gymnastics coach:

for i, v in enumerate(['a', 'skip', 'b', 'c']):
    if v == 'skip':
        continue  # Ah, skips are healthier. They say.
    print(i, v)
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Recreating enumerate

Though enumerate() is implemented in a warm, comforting cocoon of C for max speed, here's a python-inspired version for the curious minds:

def custom_enumerate(iterable, start=0):  # "They see me rollin', they hatin'"
    return zip(range(start, start + len(iterable)), iterable)
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This version behaves the same way as enumerate() but it's only functional with libraries that lend support to len().

DIY enumerate

For scenarios that are flexibly intrepid, Python's itertools.count() coupled with zip() makes enumerate() look like a do-it-yourself kit:

from itertools import count

for i, v in zip(count(10), ['a', 'b', 'c']):
    print(i, v)  # "Who needs pre-built solutions when DIY is 🔥"
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Enumerate() - the non-favorites

Circular tracks with no start or end

Enumerate() has its runners and ... non-runners. Working with sets and dict_keys that lack a well-defined order can make enumerate() less meaningful and possibly even go rogue.

The maze run

Against complex data structures, the humble enumerate() function may fall short. At times like these, traversing mechanisms custom designed for specific structure prove more formidable.

Need for speed

In performance-critical areas, enumerate()'s slight overhead may come under scrutiny.

Best practices with Enumerate()

Tracking indices

enumerate() is the poster child for eliminating the need for manual index tracking. Trust me, it’s less error-prone this way!

Embrace readability

Enumerate's bane is verbosity. Its capability to express the common pattern where both elements and their indices are needed, in a single expressive line, is truly a programmer’s gift.

Compatibility levels = 100

enumerate() fits like a glove with Python constructs, whether it's if/else within loops or the glamorous comprehensions and lambda functions.

Beast mode-on

enumerate() discards its humble Python robe for a more performant C costume, ensuring its place amongst the Python master performances.

Reference-driven learning

Brett Slatkin's "Effective Python" is an invaluable resource for enumerate() examples and the Python documentation is the encyclopedia when it comes to enumerate() and related topics.