Programming Forums > Script Programming > Python

splinter9x · Jun 9th, 2006, 6:45 PM

It was a joke but I guess by the way people posted back about it, it didn't turn out that way. Calm down and don't be like 25% of the rest of the community here and jump on someones back becouse of a post that THE READER took the wrong way.

titaniumdecoy · Jun 9th, 2006, 6:50 PM

Thanks for the tips, Cerulean.

The final function I ended up writing executed almost instantly when given a 12-digit number, as opposed to the previous function, which took over a minute.

In case anyone's interested, this problem came from a USACO challege; now I have to re-write it in C++ or Java in order to submit it. (I wrote in Python to get experience with the language.) If anyone knows of a site with Python-specific challenges, I would be very interested...

Dietrich · Jun 9th, 2006, 10:36 PM

Just to warn you, both filter() and map() will go away with Python3. As Arevos pointed out, they can be easily replaced with list comprehensions:

(Toggle Plain Text)

# write your own using list comprehension:
def map(f, s):
    return [f(x) for x in s]

def filter(f, s):
    return [x for x in s if f(s)]

Sane · Jun 10th, 2006, 7:52 AM

I find it quite silly how Python3 decided to add things like "any()" and "all()" when they are even easier to make yourself then the functions they are taking away ("filter()", "map()").

Dietrich · Jun 10th, 2006, 10:04 AM

Quote:

Originally Posted by Sane

I find it quite silly how Python3 decided to add things like "any()" and "all()" when they are even easier to make yourself then the functions they are taking away ("filter()", "map()").

Depends what you are working on.

I think filter() and map() were introduced to Python before list comprehension came around. List comprehension is probably more efficient, particularly if you use the corresponding generator.

Cerulean · Jun 12th, 2006, 12:46 PM

Quote:

Originally Posted by Dietrich

I think filter() and map() were introduced to Python before list comprehension came around. List comprehension is probably more efficient, particularly if you use the corresponding generator.

They were indeed. List comprehensions are more efficient if you're not calling a function in them. For example:

(Toggle Plain Text)

l = [104, 101, 108, 108, 111]
map(chr, l) # faster than [chr(x) for x in l] as the actual looping for the map function is done in C

[(x > 105) for x in l] # faster than map(lambda x: x > 105, l) because calling a function is fairly costly in Python.

We are talking very fractionally here, though.

Quote:

Originally Posted by Sane

I find it quite silly how Python3 decided to add things like "any()" and "all()" when they are even easier to make yourself then the functions they are taking away ("filter()", "map()").

Both are trivial one liners with list comps.

(Toggle Plain Text)

def map(func, l):
    return [func(x) for x in l]
def filter(func, l):
    return [x for x in l if func(x)]

reduce() is a fair bit harder to implement.

Jun 9th, 2006, 6:45 PM	#21
splinter9x Hobbyist Programmer Join Date: Jun 2006 Posts: 137 Rep Power: 0	It was a joke but I guess by the way people posted back about it, it didn't turn out that way. Calm down and don't be like 25% of the rest of the community here and jump on someones back becouse of a post that THE READER took the wrong way. __________________ Visit my Blog I support WINDOWS...

Jun 9th, 2006, 6:50 PM	#22
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 837 Rep Power: 3	Thanks for the tips, Cerulean. The final function I ended up writing executed almost instantly when given a 12-digit number, as opposed to the previous function, which took over a minute. In case anyone's interested, this problem came from a USACO challege; now I have to re-write it in C++ or Java in order to submit it. (I wrote in Python to get experience with the language.) If anyone knows of a site with Python-specific challenges, I would be very interested... Last edited by titaniumdecoy; Jun 9th, 2006 at 7:04 PM.

Jun 9th, 2006, 10:36 PM	#23
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	Just to warn you, both filter() and map() will go away with Python3. As Arevos pointed out, they can be easily replaced with list comprehensions: (Toggle Plain Text) # write your own using list comprehension: def map(f, s): return [f(x) for x in s] def filter(f, s): return [x for x in s if f(s)] # write your own using list comprehension: def map(f, s): return [f(x) for x in s] def filter(f, s): return [x for x in s if f(s)] __________________ I looked it up on the Intergnats!

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Jun 10th, 2006, 7:52 AM	#24
Sane Programming Guru Join Date: Apr 2005 Posts: 1,799 Rep Power: 5	I find it quite silly how Python3 decided to add things like "any()" and "all()" when they are even easier to make yourself then the functions they are taking away ("filter()", "map()").

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Programming Forums > Script Programming > Python

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