Python one-liner into normal for loop

Question

I am trying to understand the following one-liner: weights = [0.0 for i in range(len(training_data[0]))]

I would like to understand what that actually says. I think it says Append a [0.0] to the weights list for every i in the range of the length of training_data[0]

I need to convert that one-liner to a normal for loop. The following does not yield the same result, as the program I editing later complains about a numpy problem:

weights = []
num_rows = training_data[0]
for index in range(len(num_rows)):
    weights.append([0.0])

Any advice on how to convert the one-liner to a normal looking for loop is appreciated.

Answer 1

It's a list comprehension, basically you convert it like this:

weights = [0.0 for i in range(len(training_data[0]))]

into:

weights = []
total_iterations = len(training_data[0])
for i in range(total_iterations): # equivalent to for i==0, i<total_iterations, i++ in other languages
    weights.append(0.0)