[BangPypers] if not with comparision statement in python

[Dhananjay Nene]

On Mon, Aug 1, 2011 at 5:07 PM, Anand Chitipothu <anandology at gmail.com> wrote:
> 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.
>

Well, I cheated - there's one more important function (which at least
I haven't seen in the python library - flatmap)

I constructed my own version

I also constructed my own append_to_list since I didn't know how to
implement it as a lambda

Here's the code

def append_to_list(first,second) :
    l = first
    l.extend(second)
    return l

def flatmap(func, val) :
    return reduce(append_to_list, map(func,val),[])

print filter(lambda (x,y,z,pred) : pred, flatmap(lambda x:
flatmap(lambda y: flatmap(lambda z: [[x,y,z,x*x + y*y ==
z*z]],range(y,100)), range(x,100)), range(1,50)))



-- 
----------------------------------------------------------------------------------------------------------------------------------
http://blog.dhananjaynene.com twitter: @dnene google plus:
http://gplus.to/dhananjaynene