How to Efficiently Accumulate Results from Repeated Calculations in Python?

How to Accumulate Results from Repeated Calculations

Consider the following scenario: you have a calculation that assigns a value to y based on a value x. You want to perform this calculation multiple times for different values of x and collect the results in a useful data structure.

Explicit Loop

This is the most straightforward approach. Create a list or dictionary before the loop and append each calculated result to it. For instance:

def make_list_with_inline_code_and_for():
    ys = []
    for x in [1, 3, 5]:
        ys.append(x + 1)
    return ys

List Comprehension or Generator Expression

List comprehensions provide a concise way to create lists from existing sequences:

ys = [x + 1 for x in xs]

Generator expressions offer a lazy alternative to list comprehensions.

Map

Map takes a function and applies it to each element in a sequence, producing another sequence. You can use it like so:

ys = list(map(calc_y, xs))

Additional Considerations

• Use for loops for cases with existing input where each element should be processed independently.
• Use comprehension or generator expressions for applying calculations to existing sequences.
• Use map when (1) an input sequence is available, (2) the calculation requires a function or callable, and (3) the result needs to be converted into a different data structure explicitly.
• Avoid while loops for creating a fixed number of output elements; instead, generate a dummy range.
• Prefer list comprehensions over map in most cases for simplicity and flexibility.
• Generator expressions are useful when the result needs to be lazily evaluated, avoiding unnecessary memory consumption.

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