Question

I’m working through a tutorial which includes this code:

for position, target in population_gen(population):
    pos = float(position)
    all_inputs.append([random.random(), pos * factor])
    all_targets.append([target])

I don’t fully understand how the for loop works. In particular: what is the loop iterating through exactly? I’m only familiar with simple examples like for i in mylist:. How can there be a function call on the right-hand side of in, and two things separated by a comma on the left-hand side?

Answer 1

The function population_gen is returning a list of tuples, which are unpacked automatically into variable names using this syntax.

So basically, you’re getting something like the following as return value from the function:

[("pos1", "target1"), ("pos2", "target2"), ]

Given this example, in the the for loop’s first iteration, the variables “position” and “target” will have the values:

position = "pos1"
target = "target1"

In second iteration:

position = "pos2"
target = "target2"