How Can I Efficiently Store Results from Repeated Calculations in Python?

How to Collect Results of Repeated Calculations in a List or Dictionary

This question arises when we need to store the values obtained from repeated calculations using a loop or function. There are three common approaches to this problem:

Using an Explicit Loop:

Create a list or dictionary before the loop and add each computed value to it:

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

This method is straightforward and works well with both for loops and while loops.

Using a Comprehension or Generator Expression:

• List Comprehension: Allows us to create a list directly from an existing sequence of values using an expression:

ys = [x + 1 for x in [1, 3, 5]]

• Dict Comprehension: Similarly creates a dictionary from a sequence by specifying both a key and a value expression:

ys = {x: x + 1 for x in [1, 3, 5]}

Using the map Function:

map applies a specified function to each element in an iterable (list, tuple, etc.):

def calc_y(x):
    return x + 1

xs = [1, 3, 5]
ys = list(map(calc_y, xs))

map returns an iterator that can be converted to a list, set, or dictionary.

Additional Considerations:

• Use a for loop when you have an existing input sequence or need to process each element independently.
• Use a while loop to generate output elements until a specific condition is met.
• Use comprehensions for clarity and efficiency when working with existing sequences.
• Use map when you need to apply a function to a sequence without worrying about the iteration variable.

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