Forums: » Register « |  Free Tools |  User CP |  Games |  Calendar |  Members |  FAQs |  Sitemap |  Support |

New Free Tools on Dev Shed!

#1
January 1st, 2013, 08:38 PM
 MickeyCoder
Registered User

Join Date: Jan 2013
Posts: 2
Time spent in forums: 21 m 4 sec
Reputation Power: 0
Working program but review required to make it better

Hi All,

I just started learning Python using online resources and am just a couple of days old in it. I have quite a good experience in Java though (10+ years) and Python caught my fancy during the Christmas holidays as had nothing better to do

I wrote a quick and dirty code to compute factorial of a number using Python and I need an expert's opinion about it with respect to the structure and semantics - is there something that can be more optimized in it, something that was done incorrectly etc. Am interested to learn the language right the first time, and will immensely appreciate any feedback.

The idea of code is simple - being a recursive algorithm, I've tried to cache all previously computed values of factorial in a file which is cached when an object of FactCache is created. Factorial then uses the cache to reduce recursion.

Code follows:

Code:
```import os
import pickle
"""
Caches and pickles factorial of a number.
Upon instantiation, sarches for the file 'fact.cache'
in the current directory or in the path passed during
If found then unpickles it and creates the dictionary
with pre-calculated factorial values.
"""
class FactCache:
c = {}
def __init__(self,path="./fact.cache"):
self.path=path
try:
if(os.path.isfile(self.path)):
print("Cache file found. Reading it now...")
else:
with open(self.path,'wb') as writeCache:
pickle.dump(self.c,writeCache)
except IOError as err:
pass
finally:
print(self.c)

"""
Stores the value (f) of the factorial for a number (n) in the file.
"""
self.c[n]=f
with open(self.path,'wb') as writeCache:
pickle.dump(self.c,writeCache)

"""
Returns the value of the factorial for a number (n) from the dictionary.
"""
def get(self,n):
if n in self.c:
return self.c[n]
else:
return -1

"""
Computes factorial of a given number and
reuses all previous results to reduce recursion.
"""
def factorial(n,c):
f = c.get(n)
if(f == -1):
if(n==0):
return 1
else:
v = n*factorial(n-1,c)
return v
else:
print("Value served from cache for ",n)
return f```

Output follows:
>>> factorial(26,c)
Value served from cache for 25
403291461126605635584000000

#2
January 1st, 2013, 09:57 PM
 b49P23TIvg
Contributing User

Join Date: Aug 2011
Posts: 4,118
Time spent in forums: 1 Month 3 Weeks 2 Days 3 h 38 m 25 sec
Reputation Power: 455
Wonderful.

Next write a decorator to hide the cache argument.
__________________
[code]Code tags[/code] are essential for python code!

#3
January 2nd, 2013, 07:04 AM
 SuperOscar
Contributing User

Join Date: Jul 2007
Location: Joensuu, Finland
Posts: 420
Time spent in forums: 1 Week 18 h 21 m 33 sec
Reputation Power: 66
Quote:
 Originally Posted by MickeyCoder Am interested to learn the language right the first time, and will immensely appreciate any feedback.

Docstrings should go below the thing they document, not (as in Ruby) above. Also, PEP 257 recommends that the first line is followed by a blank line. I.e.:

Code:
```def spam(eggs):

A more detailed explanation follows here.
'''```
__________________
My armada: openSUSE 13.1 (home desktop, home laptop), Ubuntu 13.04 (work laptop), FreeBSD 9.2 (server), Mythbuntu 12.04 LTS (HTPC), Bodhi Linux 2.0 & Windows 7 Ultimate (test desktop), Android 4.1.2 (tablet)

#4
January 2nd, 2013, 01:29 PM
 Dietrich
Contributing User

Join Date: Feb 2005
Posts: 570
Time spent in forums: 5 Days 2 h 20 m 45 sec
Reputation Power: 63
You can also access a properly located documentation string this way:
Code:
```''' DocumentationString1.py
documentation strings must be added right below the function definition,
triple quotes are recommended as a standard
can be accessed via function_name.__doc__
'''

def get_distance(x1, y1, x2, y2):
"""
get_distance(x1, y1, x2, y2)
returns distance between two points using the pythagorean theorem
the function parameters are the coordinates of the two points
"""
dx = x2 - x1
dy = y2 - y1
return (dx**2 + dy**2)**0.5

#
# since the indentation rules relax between triple quotes
# you can also use this to avoid adding spaces in front of
# the doc string
#

def get_distance2(x1, y1, x2, y2):
"""
get_distance(x1, y1, x2, y2)
returns distance between two points using the pythagorean theorem
the function parameters are the coordinates of the two points
"""
dx = x2 - x1
dy = y2 - y1
return (dx**2 + dy**2)**0.5

print( "The function's documentation string:" )
# shows text between the triple quotes
print(get_distance.__doc__)
print(get_distance2.__doc__)

''' my result >>>
The function's documentation string:

get_distance(x1, y1, x2, y2)
returns distance between two points using the pythagorean theorem
the function parameters are the coordinates of the two points

get_distance(x1, y1, x2, y2)
returns distance between two points using the pythagorean theorem
the function parameters are the coordinates of the two points
'''```
__________________
Real Programmers always confuse Christmas and Halloween because Oct31 == Dec25

#5
January 2nd, 2013, 05:12 PM
 MickeyCoder
Registered User

Join Date: Jan 2013
Posts: 2
Time spent in forums: 21 m 4 sec
Reputation Power: 0
Thanks!

Thank you all for your feedback. @b49P23TIvg: The decorators are very interesting and thanks for pointing me in that direction!

#6
January 2nd, 2013, 05:58 PM
 Dietrich
Contributing User

Join Date: Feb 2005
Posts: 570
Time spent in forums: 5 Days 2 h 20 m 45 sec
Reputation Power: 63
A decorator would be a little overkill since it would only be useful for that particular function.

 Viewing: Dev Shed Forums > Programming Languages > Python Programming > Working program but review required to make it better