How Have `filter`, `map`, and `reduce` Changed in Python 3?

Python 3: Variations in the Implementation of Filter, Map, and Reduce

In Python 2, filter, map, and reduce behave differently from their Python 3 counterparts. This stems from several significant changes implemented in Python 3:

Views and Iterators Over Lists:

• map() and filter() now return iterators instead of lists. To obtain a list, explicitly convert them using list().

Removal of reduce():

• reduce() has been removed from core Python in favor of the functools.reduce() function. However, an explicit for loop is typically more readable and preferred.

Example Usage:

The Python 2 code snippets can be updated for Python 3 as follows:

def f(x):
    return x % 2 != 0 and x % 3 != 0

# **Filter:** Use list() to obtain a list of filtered values
filtered_list = list(filter(f, range(2, 25)))

# **Map:** Similarly, use list() to convert the iterator to a list
cubed_list = list(map(lambda x: x ** 3, range(1, 11)))

# **Reduce:** Use functools.reduce() or an explicit for loop
from functools import reduce
add_result = reduce(lambda x, y: x + y, range(1, 11))

print(filtered_list)  # Output: [5, 7, 11, 13, 17, 19, 23]
print(cubed_list)   # Output: [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
print(add_result)   # Output: 55

Additional Resources:

• [Python 3.0 Changes](https://docs.python.org/3/whatsnew/3.0.html)
• [map() and Views](https://wiki.python.org/moin/Getting a map() to return a list in Python 3.x)

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