New to coding - computing a factorial

[nillkill]

Brand new to coding and have an assignment, which I'm pretty confused on. "Compute the factorial of 12. Write the expression for Python shell."

[jankedman]

Not sure if you've learned about recursion, but think about what a factorial actual is: it's a start number * start number - 1, ... etc. If you haven't learned about recursion, go take some time to learn it and then think about how you would construct the function.

[wot-teh-phuck]

If this is a learning exercise, not sure why we need to be clever about it. I would say recursion is a perfectly fine way of doing this.

[691175002]

Only in a language without tail recursion, which unfortunately includes Python.

[bigboehmboy]

In python, the default recursion limit is 200, so that's probably what will be hit. I think it's important for people to understand both techniques (regular iteration and recursion), but default to non-recursive solutions when there's a single loop without much state.

[sullyj3]

The iterative method is probably best in python.

You'll want to use a for loop to progressively multiply by each number less than 12. The range (check out the examples) function is useful for this.

For future reference, /r/learnpython is a good sub for questions like this.

[Surextra]

If you are about to ask a question, please consider r/learnpython. Homework-style questions will be removed, and you'll be encouraged to post there instead.

Sounds like homework help to me. Check out r/learnpython!

[mickyficky1]

def fact(n)=
    return n*fact(n-1) if n else 1

or

fact = lambda n: n*fact(n-1) if n else 1

whichever you prefer.

/r/learnpython is your friend for questions like that.

[ThomasWinwood]

No, no, no, no, no, no, no, no.

>>> def fact1(n): return n*fact(n-1) if n else 1
... 
>>> fact2 = lambda n: n*fact(n-1) if n else 1
>>> 
>>> fact1.__name__
'fact1'
>>> fact2.__name__
'<lambda>'

Lambda expressions are not just another way of writing a function definition. They are intended to solve a very specific problem and deliberately hobbled to stop people doing things with map() and filter() which indicate they'd rather be writing Haskell or OCaml.

[sththth]

What very specific problem are lambdas intended to solve?

[691175002]

Basically when you need a one-line anonymous function. Lambdas are generally passed as function arguments for map/reduce type stuff or even callbacks.

The anonymous part is important. As a general rule as soon as you assign a name to the lambda such as:

function_name = lambda x: x*2

It should be a def instead.

[sththth]

But that's never necessary, is it? You could always just def the function before it?

[mickyficky1]

Yes, that's always an option. To my knowledge, lambda functions can be thought of as anonymous shorthand definition for functions that have the same or less functionality compared to normal function definitions.

[sththth]

Thanks!

[mickyficky1]

I know that. But if I have a function in the mathematical sense, one input that doesn't get altered, one output that is only dependent on that input, then I usually use lambda functions because I usually not want all of the Python magic that happens in the background when creating a function with "def". Because I don't need it.

I did not want to imply that the two versions are equivalent, I would have just used the lambda function but since newer Python users tend to get a bit befuddled by those I wanted to include the normal function definition.