[BangPypers] if not with comparision statement in python

[Anand Chitipothu]

2011/8/1 Dhananjay Nene <dhananjay.nene at gmail.com>:
> On Mon, Aug 1, 2011 at 4:17 PM, Anand Chitipothu <anandology at gmail.com> wrote:
>> 2011/8/1 Dhananjay Nene <dhananjay.nene at gmail.com>:
>>> On Sat, Jul 30, 2011 at 2:15 PM, Asif Jamadar <asif.jamadar at rezayat.net> wrote:
>>>> What if I have two lists for both minimum and maximum values
>>>>
>>>> Minimum  Maximum
>>>> 0               10
>>>> 11              20
>>>> 21              30
>>>> 31              40
>>>>
>>>>
>>>> Now how should I check if actual result is not laying between above ranges
>>>>
>>>> if not minimum<=actual_result and  not maximum>=actual_result:
>>>>
>>>> Any suggestions?
>>>
>>> def in_range(number) :
>>>    return any(map(lambda (x,y) : x <= number <= y,
>>>                  ((0,10),(11,20), (21,30), (31,40))))
>>
>> How about this?
>>
>> def in_range(number, min_max_pairs):
>>    return any(x <= number <=y for x, y in min_max_pairs)
>
> Definitely better
>>
>> List comprehensions and generation expressions are usually more
>> readable and expressive than using map.
>
> Thats probably truer for the python and python trained eyes than any
> other (in other words its both subjective and contextual and a bit to
> do with syntax). Allow me to illustrate :
>
> If I want to double all elements in a list and then increment them by
> one, here's how I would use a map in python
>
> def double(x) : return x * 2
> def increment(x) : return x + 1
> print map(increment,map(double,range(5)))
>
> and here's how I would do it in scala - notice the last (third) line
> and consider its readability (I'm sure a scala non-novice will offer
> something even superior)
>
> def double(n: Int) = n * 2
> def increment(n: Int) = n + 1
> println(0 to 4 map double map increment)
>
> so readability is often a function of what one's eyes are trained ot
> read and also the syntactic capabilities in the language

This is just the prefix/postfix thing.

Yes, prefix style is difficult to read if there are too many nested
levels. Look at lisp code for example. Yes, it feel it awkward when I
have to do range(len(x)). Unix pipes and chaining methods are postfix.
What you are doing in scala is just that.

If map was a list method, I could do this:

range(0, 4).map(douple).map(increment)

And as unix pipe:

seq 0 4 | double | increment

> I also find map much more atomic and portable construct to think in -
> after all every list comprehension is syntactic sugar around map +
> filter, and map/reduce/filter are far more omnipresent than list
> comprehensions.

Recently, I was thinking about converting a list comprehension to
map/filter calls and It turned out that list comprehensions are more
than map+filter.

[i * i for i in range(10)]  ~ map(lambda i*i, range(10))

[i * i for i in range(10) if i % 2 == 0] ~  map(lambda i*i,
filter(lambda i%2 == 0, range(10)))

But the situation gets tricky when there are multiple loop items in
the list comprehension.

Here is a list comprehension to find all Pythagorean triplets below 100.

[(x, y, z) for x in range(1, 50) for y in range(x, 100) for z in
range(y, 100) if x*x + y*y == z*z]

Try converting this into map/filter and you'll understand the difference.

Anand