Iteration for Factorials

[Py-Fun]

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

[Diez B. Roggisch]

Re: Iteration for Factorials

Py-Fun wrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

Show us your attempts, and we might suggest a fix. Because otherwise this
sounds suspiciously like homework.

Diez

[Py-Fun]

Re: Iteration for Factorials

On 22 Oct, 13:28, "Diez B. Roggisch" <de...@nospam.w eb.dewrote:

Py-Fun wrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

>
Show us your attempts, and we might suggest a fix. Because otherwise this
sounds suspiciously like homework.
>
Diez

Here is my futile attempt. Be careful with this though, I just ran
something similar and it was never ending...

def itforfact(n):
while n<100:
print n
n+1
n = input("Please enter a number below 100")

itforfact(n)

[Marco Mariani]

Re: Iteration for Factorials

Py-Fun wrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

As opposed to what, a complicated one?

[Marco Mariani]

Re: Iteration for Factorials

Py-Fun wrote:

def itforfact(n):
while n<100:
print n
n+1
n = input("Please enter a number below 100")

You function should probably return something. After that, you can see
what happens with the result you get.

[Duncan Booth]

Re: Iteration for Factorials

Py-Fun <lorna.burns@gm ail.comwrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.
>

This version avoids doing anything fancier than adding 1, so it should be
simple enough for anyone:

def factorial(e):
a = 1
for b in range(e):
c = 0
for j in range(b, -1, -1):
for d in range(a):
c += 1
a = c
return a

[Py-Fun]

Re: Iteration for Factorials

On 22 Oct, 13:43, Marco Mariani <ma...@sferacar ta.comwrote:

Py-Fun wrote:

def itforfact(n):
while n<100:
print n
n+1
n = input("Please enter a number below 100")

>
You function should probably return something. After that, you can see
what happens with the result you get.

Marco, Thanks for the tip. This now works:

def itforfact(n):
while n<100:
print n
n = n+1
n = input("Please enter a number below 100")

itforfact(n)

Is it a "factorial" though?

[cokofreedom@gmail.com]

Re: Iteration for Factorials

On Oct 22, 2:43 pm, Marco Mariani <ma...@sferacar ta.comwrote:

Py-Fun wrote:

def itforfact(n):
while n<100:
print n
n+1
n = input("Please enter a number below 100")

>
You function should probably return something. After that, you can see
what happens with the result you get.

lambda n: n<=0 or reduce(lambda a,b: long(a)*long(b) ,xrange(1,n+1))

[Amit Khemka]

Re: Iteration for Factorials

On 10/22/07, Py-Fun <lorna.burns@gm ail.comwrote:

On 22 Oct, 13:28, "Diez B. Roggisch" <de...@nospam.w eb.dewrote:

Py-Fun wrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

Show us your attempts, and we might suggest a fix. Because otherwise this
sounds suspiciously like homework.

Diez

>
Here is my futile attempt. Be careful with this though, I just ran
something similar and it was never ending...
>
def itforfact(n):
while n<100:
print n
n+1
n = input("Please enter a number below 100")
>
itforfact(n)

Let me give you a pseudo code (which though can be found in most of
the textbooks and some 'simple' googling). Try to understand the code
and then write an equivalent python function.

function iFactorial(n: integer): integer;
var i, temp: integer;
begin
temp = 1;
for i = 1 to n do
temp = temp * i
end
return temp

About your code.
1. why doesn't it surprise you if the code that you posted goes in
infinite loop ?!
2. why do you use condition: n < 100
3. How do you think that your function will calculate the factorial ?
4. Instead of "input" use "raw_input" , and then "cast" the input as integer .

Cheers,
amit.
--
--
Amit Khemka

[vimal]

Re: Iteration for Factorials

On Oct 22, 5:43 pm, Marco Mariani <ma...@sferacar ta.comwrote:

Py-Fun wrote:

def itforfact(n):
while n<100:
print n
n+1
n = input("Please enter a number below 100")

>
You function should probably return something. After that, you can see
what happens with the result you get.

i am just suggesting u an idea
but i dont know it satisfies ur needs

x=10
def cal_range(10)
for i in range(10):
print 2**i

[Ant]

Re: Iteration for Factorials

On Oct 22, 1:26 pm, Py-Fun <lorna.bu...@gm ail.comwrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

The following simple adder functions should give you an idea of how
recursion can be recast as iteration:

def acc(i):
'''i should be a positive integer'''
if i 0:
return i + acc(i - 1)
return 0

print "acc", acc(9)

def itt(i):
'''i should be a positive integer'''
out = 0

while i 0:
out += i
i = i - 1

return out

print "itt", itt(9)

...
Is it a "factorial" though?

Er, no. And neither is mine. You may want to google for the definition
of factorial! Here's a hint:

reduce(operator .mul, range(1, i + 1))

--
Anthony Roy

[Marco Mariani]

Re: Iteration for Factorials

From the cookbook, this time.
It satisfies the requirements nicely ;)

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/496691

def tail_recursion( g):
'''
Version of tail_recursion decorator using no stack-frame
inspection.
'''
loc_vars ={"in_loop":Fal se,"cnt":0}

def result(*args, **kwd):
loc_vars["cnt"]+=1
if not loc_vars["in_loop"]:
loc_vars["in_loop"] = True
while 1:
tc = g(*args,**kwd)
try:
qual, args, kwd = tc
if qual == 'continue':
continue
except (TypeError, ValueError):
loc_vars["in_loop"] = False
return tc
else:
if loc_vars["cnt"]%2==0:
return ('continue',arg s, kwd)
else:
return g(*args,**kwd)
return result


@tail_recursion
def factorial(n, acc=1):
"calculate a factorial"
if n == 0:
return acc
res = factorial(n-1, n*acc)
return res

[Tim Golden]

Re: Iteration for Factorials

Marco Mariani wrote:

From the cookbook, this time.
It satisfies the requirements nicely ;)
>
>

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/496691

>

[... snip the ultimate general-purpose answer to the OP's question ...

I really hope that's a wink up there, Marco. The poor guy
was just trying to get his homework done!

:>

TJG

[Marco Mariani]

Re: Iteration for Factorials

Tim Golden wrote:

> From the cookbook, this time.
>It satisfies the requirements nicely ;)
>>
>http://aspn.activestate.com/ASPN/Coo.../Recipe/496691

>
[... snip the ultimate general-purpose answer to the OP's question ...
>
I really hope that's a wink up there, Marco.

The wink is in the second line of my post... more for the "do the least
amount of work to meet the requirements" people that for the OP

The poor guy was just trying to get his homework done!

I don't see how my answer is in any way worse than those based on
lambda. Maybe I'm just envious because when I was his age I couldn't
google for answers. He should at least be able to do that, shouldn't he?
But wait. That would mean understanding what a factorial is. That would
require a second search, or a textbook, or an understanding of
arithmetics before programming with or without recursion. Should we
blame the teachers?

[Peter Goodman]

Re: Iteration for Factorials

On Oct 22, 8:26 am, Py-Fun <lorna.bu...@gm ail.comwrote:

I'm stuck trying to write a function that generates a factorial of a
number using iteration and not recursion. Any simple ideas would be
appreciated.

def fac_btt(num):
total = 1
if num 1:
for i in range(1, num+1):
total *= i
return total