[BangPypers] diffrerence between lambda function and ordinary one
i was writing some basic code . for understanding lambda functions , but couldnt understand the difference between a lambda function and an ordinary function. for example >>>def f (x): return x**2 ... >>> print f(8) >>> 64 >>> g = lambda x: x**2 >>> >>> print g(8) >>> 64 wats a need for using lambda functions ..? ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] diffrerence between lambda function and ordinary one
> > > i was writing some basic code . for understanding lambda functions , but > couldnt understand the difference between a lambda function and an ordinary > function. > > for example > > >>>def f (x): return x**2 > ... > >>> print f(8) > >>> 64 > >>> g = lambda x: x**2 > >>> > >>> print g(8) > >>> 64 > > wats a need for using lambda functions ..? > Lambda functions are generally used where you need one liner functions to get things done. It was a feature which was considered for removal in py3k but there were too many people who loved the feature. :) Personally I feel that lambda functions are great as long as they are readable. zm ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] diffrerence between lambda function and ordinary one
2010/8/6 Rahul R :
> i was writing some basic code . for understanding lambda functions , but
> couldnt understand the difference between a lambda function and an ordinary
> function.
>
> for example
>
def f (x): return x**2
> ...
print f(8)
64
g = lambda x: x**2
print g(8)
64
>
> wats a need for using lambda functions ..?
Lambda functions are expressions. You can define a lambda function
inside a function call or a dictionary definition, which is not
possible with regular functions. For example:
d.sort(key=lambda x: x.lower())
functions = {
"lower": lambda k: k.lower(),
"upper": lambda k: k.upper()
}
Anand
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Re: [BangPypers] diffrerence between lambda function and ordinary one
On Fri, Aug 6, 2010 at 10:20 AM, Rahul R wrote: > i was writing some basic code . for understanding lambda functions , but > couldnt understand the difference between a lambda function and an ordinary > function. > > for example > def f (x): return x**2 > ... print f(8) 64 g = lambda x: x**2 print g(8) 64 > > wats a need for using lambda functions ..? You mean "what's the need for using lambda functions?" Lambda functions are anonymous functions, ie., functions without a name. Along with map, reduce, filter, lambda functions provide functional programming[1] constructs to python. You can write code like this: from operator import add print reduce(add, filter(lambda x: x%2==0, xrange(10))) to print the sum of even numbers less than 10 instead of: tot = 0 for i in xrange(10): if i%2 == 0: tot += i print tot ... Anyway, One does not "need" to use lambda function. Almost in all the places where you use lambda functions, you can replace it with a named function with added benefit of clarity. Python lambdas are limited to a single statement, which makes them particularly hobbled. Guido is not very fond of FP constructs, in fact he wanted to remove them from python 3. After much discussion, lambda survived in Py3. [1] http://en.wikipedia.org/wiki/Functional_programming ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] python speed comparison
>
>
>
> Your python code as is clocked about 72 seconds on my notebook. The
> following came in at about 4.6 seconds (just has a small trick of reusing
> earlier results)
>
> import time
> start =time.time()
> longest = None
> longest_elements = 0
> solved = {}
> for val in xrange(1,100) :
>counter = 1
>number = val
>while number != 1 :
>number = number / 2 if number % 2 == 0 else 3 * number + 1
>if number in solved :
>counter = counter + solved[number]
>break
>else :
>counter = counter + 1
>if counter > longest_elements :
>longest_elements = counter
>longest = val
>solved[val] = counter
> end = time.time()
> print "Time:", end - start
> print longest, ':', longest_elements
>
> Dhananjay
>
>
If you are still looking forward to squeeze around 200ms more, try bit ops -
Original code by Dhananjay averages to 4.25823163986s on my machine
While if you change -
number = number / 2 if number % 2 == 0 else 3 * number + 1
into
number = 3*number+1 if number&1 else number >> 1
it averages 4.058642069496667s on my machine.
Abhishek
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Re: [BangPypers] diffrerence between lambda function and ordinary one
> > > > You can write code like this: > > from operator import add > print reduce(add, filter(lambda x: x%2==0, xrange(10))) > > to print the sum of even numbers less than 10 > instead of: > tot = 0 > for i in xrange(10): > if i%2 == 0: > tot += i > print tot > > ... > I would prefer LC anyway: >>> sum(i for i in range(0,10,2)) 20 -- ~l0nwlf ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] diffrerence between lambda function and ordinary one
On Fri, Aug 6, 2010 at 10:45 AM, Shashwat Anand wrote: > I would prefer LC anyway: > sum(i for i in range(0,10,2)) > 20 why use LC at all? >> sum(range(0,10,2)) ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] diffrerence between lambda function and ordinary one
On Fri, Aug 6, 2010 at 8:37 PM, Pradeep Gowda wrote: > On Fri, Aug 6, 2010 at 10:45 AM, Shashwat Anand > wrote: > > I would prefer LC anyway: > > > sum(i for i in range(0,10,2)) > > 20 > > why use LC at all? > >> sum(range(0,10,2)) > Oops. Wrong choice of example. -- ~l0nwlf ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] python speed comparison
Readability counts. Here is my attempt.
def memoize(f):
cache = {}
def g(a):
if a not in cache:
cache[a] = f(a)
return cache[a]
return g
@memoize
def solve(n):
if n == 1:
return 1
elif n%2 == 0:
return 1 + solve(n/2)
else:
return 1 + solve(3*n+1)
print max((solve(i), i) for i in range(1, 1+100))
$ time python p14.py
(525, 837799)
real0m3.981s
user0m3.728s
sys 0m0.242s
Anand
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Re: [BangPypers] diffrerence between lambda function and ordinary one
On Fri, Aug 6, 2010 at 8:37 PM, Pradeep Gowda wrote: > On Fri, Aug 6, 2010 at 10:45 AM, Shashwat Anand > wrote: > > I would prefer LC anyway: > > > sum(i for i in range(0,10,2)) > > 20 > > why use LC at all? > >> sum(range(0,10,2)) > > ^ I too have written such "i for i in ..." expressions at times and I feel enlightened now. ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
Re: [BangPypers] diffrerence between lambda function and ordinary one
This would serve a better example - >>> sum( int(x) for x in raw_input().split() ) 1 2 3 4 10 >>> ___ BangPypers mailing list BangPypers@python.org http://mail.python.org/mailman/listinfo/bangpypers
