Re: [Tutor] Map function
Hi Phil,
On 2013-08-10 16:45, Phil wrote:
> The Arduino has a map function named "map" which looks like this:
>
> map(value, 0, 1023, 0, 100)
>
> The function, in this case, takes an integer value between 0 and
> 1023 and returns a number between 0 and 100. Is there a Python
> equivalent?
The Arduino documentation[0] says that `map' is equivalent to:
long map(long x, long in_min, long in_max, long out_min, long out_max) {
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}
With that in mind, you can almost copy and paste the exact same code in Python
(albeit with floor division, as in Python 3, integer division can yield
floats). Note that `//' is not strictly equivalent to C's integer division,
though.[1]
>>> def arduino_map(x, in_min, in_max, out_min, out_max):
... return (x - in_min) * (out_max - out_min) // (in_max - in_min) +
out_min
...
>>> arduino_map(50, 0, 1023, 0, 100)
4
0: http://arduino.cc/en/Reference/map
1: http://stackoverflow.com/a/5365702/945780
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Re: [Tutor] Python Programming for the absolute beginner 3e, Ch3 Challenge 4
Also don't know how to do a binary chop, but the book hasn't covered anything
>like that - it has just taught if, else and while,
>
>A binary chop is an algorithm. All you need is if/else and while.
The algorithm looks a bit like this:
while not found
determine the middle value between min and max
if value > target set max to value
if value < target set min to value
else found = True
the_number = int(input("Type in a number - I swear down I no look!^^ "))You
don't need to store the number since the human user can just remember it
print("But I asked the computer, and it reckons your number is...")
>
>guess = (random.randint(1, 100))You don't want to use random guesses - that
>could take a very long time!
while guess != the_number:
>
> hilo = input("\nWas I too high or too low? Write 'h' or 'l'.\n")
> if hilo == "h":
> print("\nToo high, well, in that case what about...\n")
> lower_guess = (random.randint(lowest, temp))This is almost right
>except you will be faster using the mid value rather than a random one.
And what happened in the shell:
>
>
>
>Hello & Welcome to 'Modified Guess My Number'!
>
>
>Think of a number between 1 and 100 & the computer has to guess it.
>Type in a number - I swear down I no look!^^ 30
>OK you wrote 30 but I no show the computer.
>
>
>But I asked the computer, and it reckons your number is...
>57
>
>
>Was I too high or too low? Write 'h' or 'l'.
>h
>
>
>Too high, well, in that case what about...
>
>
>10
>
>
>Was I too high or too low? Write 'h' or 'l'.
>l
>
>
>Too low, well, in that case what about...
>
>
>53
>
>
>Was I too high or too low? Write 'h' or 'l'.
>h
>
>
>Too high, well, in that case what about...
>
>
>51
>
>
>Was I too high or too low? Write 'h' or 'l'.
>hAs you can see its working, but just taking a lot of guesses.
You will speed it up dramatically if you calculate the mid
point rather than use random.
HTH
Alan G.___
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