# What does 1. mean here?

here the author wrote ` cost = (1./m) * (-np.dot(Y,np.log(AL).T) - np.dot(1-Y, np.log(1-AL).T))` what does 1. do here instead of just 1 ?

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`1.` or `1.0` is a float and `1` is an integer. Python stuff. If your data is integer but your calculation includes decimal points, you will get error.

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Exactly. It used to be the case that python (back in the 2.x days) required you to be very careful about that. In python 2.x, if you wrote this:

``````m = 5
x = 1 / m
``````

The answer would end up being integer 0. The reason is that both of the operands to / are integers, so the result is coerced to an integer also. I forget whether they did â€śfloorâ€ť or â€śroundâ€ť, but you get an integer result.

They fixed this in python 3.x by changing the rules. But a lot of people got into the habit of being safe by making sure that the constants you use are float, when thatâ€™s what you mean. So even in python 2.x, writing this will give 0.2:

``````m = 5.
x = 1. / m
``````

Might as well be safe and write it in a way that works whatever version of python you are running.

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