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comp.lang.python

case do problem

Tracubik

3/2/2010 5:46:00 PM

hi, i've to convert from Pascal this code:

iterations=0;
count=0;
REPEAT;
iterations = iterations+1;
...
IF (genericCondition) THEN count=count+1;
...
CASE count OF:
1: m = 1
2: m = 10
3: m = 100
UNTIL count = 4 OR iterations = 20

i do something like this:

iterations = 0
count = 0

m_Switch = (1,10,100)

while True:
iterations +=1
...
if (genericCondition):
count +=1
...
try:
m = m_Switch[count-1]
except: pass
if count = 4 or iterations = 20

the problem is that when count = 4 m_Switch[4-1] have no value, so i use
the try..except.

Is there a better solution to solve this problem? and, generally
speaking, the try..except block slow down the execution of the program or
not?

Thank you in advance
Nico
12 Answers

Tracubik

3/2/2010 5:51:00 PM

0

additional information:

when count=4 i haven't to change the m value, so i have to do nothing or
something like m = m

Nico

Alf P. Steinbach

3/2/2010 6:00:00 PM

0

* Tracubik:
> hi, i've to convert from Pascal this code:
>
> iterations=0;
> count=0;
> REPEAT;
> iterations = iterations+1;
> ...
> IF (genericCondition) THEN count=count+1;
> ...
> CASE count OF:
> 1: m = 1
> 2: m = 10
> 3: m = 100

Uhm, is this syntactically valid Pascal? As I recall, every Pascal construct was
delimited in some way. Once I had the complete Pascal syntax in my head, but
alas, not anymore...


> UNTIL count = 4 OR iterations = 20
>
> i do something like this:
>
> iterations = 0
> count = 0
>
> m_Switch = (1,10,100)
>
> while True:
> iterations +=1
> ...
> if (genericCondition):
> count +=1
> ...
> try:
> m = m_Switch[count-1]
> except: pass
> if count = 4 or iterations = 20
>
> the problem is that when count = 4 m_Switch[4-1] have no value, so i use
> the try..except.

iterations = 0
count = 0
while not( count == 4 or iterations == 20 ):
iterations += 1
# ...
if generic_condition:
count += 1
# ...
m = (1, 10, 100, 100)[count]


> Is there a better solution to solve this problem?

Define "better". Do you mean faster, more clear, shorter, using less memory, what?

Above I've assumed that you want to get rid of the try block, since that's what
you're asking about:


> and, generally
> speaking, the try..except block slow down the execution of the program or
> not?

Probably, but don't think about it. Python programming is at a level where that
kind of efficiency doesn't count. Or, ideally it shouldn't count.


Cheers & hth.,

- Alf

Alf P. Steinbach

3/2/2010 6:02:00 PM

0

* Alf P. Steinbach:
> * Tracubik:
>> hi, i've to convert from Pascal this code:
>>
>> iterations=0;
>> count=0;
>> REPEAT;
>> iterations = iterations+1;
>> ...
>> IF (genericCondition) THEN count=count+1;
>> ...
>> CASE count OF:
>> 1: m = 1
>> 2: m = 10
>> 3: m = 100
>
> Uhm, is this syntactically valid Pascal? As I recall, every Pascal
> construct was delimited in some way. Once I had the complete Pascal
> syntax in my head, but alas, not anymore...
>
>
>> UNTIL count = 4 OR iterations = 20
>>
>> i do something like this:
>>
>> iterations = 0
>> count = 0
>>
>> m_Switch = (1,10,100)
>>
>> while True:
>> iterations +=1
>> ...
>> if (genericCondition):
>> count +=1
>> ...
>> try:
>> m = m_Switch[count-1]
>> except: pass
>> if count = 4 or iterations = 20
>>
>> the problem is that when count = 4 m_Switch[4-1] have no value, so i
>> use the try..except.
>
> iterations = 0
> count = 0
> while not( count == 4 or iterations == 20 ):
> iterations += 1
> # ...
> if generic_condition:
> count += 1
> # ...
> m = (1, 10, 100, 100)[count]

Add one extra 100 there.


>> Is there a better solution to solve this problem?
>
> Define "better". Do you mean faster, more clear, shorter, using less
> memory, what?
>
> Above I've assumed that you want to get rid of the try block, since
> that's what you're asking about:
>
>
>> and, generally speaking, the try..except block slow down the execution
>> of the program or not?
>
> Probably, but don't think about it. Python programming is at a level
> where that kind of efficiency doesn't count. Or, ideally it shouldn't
> count.
>
>
> Cheers & hth.,
>
> - Alf

Alf P. Steinbach

3/2/2010 6:04:00 PM

0

* Alf P. Steinbach:
> * Alf P. Steinbach:
>> * Tracubik:
>>> hi, i've to convert from Pascal this code:
>>>
>>> iterations=0;
>>> count=0;
>>> REPEAT;
>>> iterations = iterations+1;
>>> ...
>>> IF (genericCondition) THEN count=count+1;
>>> ...
>>> CASE count OF:
>>> 1: m = 1
>>> 2: m = 10
>>> 3: m = 100
>>
>> Uhm, is this syntactically valid Pascal? As I recall, every Pascal
>> construct was delimited in some way. Once I had the complete Pascal
>> syntax in my head, but alas, not anymore...
>>
>>
>>> UNTIL count = 4 OR iterations = 20
>>>
>>> i do something like this:
>>>
>>> iterations = 0
>>> count = 0
>>>
>>> m_Switch = (1,10,100)
>>>
>>> while True:
>>> iterations +=1
>>> ...
>>> if (genericCondition):
>>> count +=1
>>> ...
>>> try:
>>> m = m_Switch[count-1]
>>> except: pass
>>> if count = 4 or iterations = 20
>>>
>>> the problem is that when count = 4 m_Switch[4-1] have no value, so i
>>> use the try..except.
>>
>> iterations = 0
>> count = 0
>> while not( count == 4 or iterations == 20 ):
>> iterations += 1
>> # ...
>> if generic_condition:
>> count += 1
>> # ...
>> m = (1, 10, 100, 100)[count]
>
> Add one extra 100 there.

Oh dear, it's one of those days.

if 1 <= count <= 3:
m = (1, 10, 100)[count - 1]


>>> Is there a better solution to solve this problem?
>>
>> Define "better". Do you mean faster, more clear, shorter, using less
>> memory, what?
>>
>> Above I've assumed that you want to get rid of the try block, since
>> that's what you're asking about:
>>
>>
>>> and, generally speaking, the try..except block slow down the
>>> execution of the program or not?
>>
>> Probably, but don't think about it. Python programming is at a level
>> where that kind of efficiency doesn't count. Or, ideally it shouldn't
>> count.
>>
>>
>> Cheers & hth.,
>>
>> - Alf

MRAB

3/2/2010 6:26:00 PM

0

Tracubik wrote:
> hi, i've to convert from Pascal this code:
>
> iterations=0;
> count=0;
> REPEAT;
> iterations = iterations+1;
> ...
> IF (genericCondition) THEN count=count+1;
> ...
> CASE count OF:
> 1: m = 1
> 2: m = 10
> 3: m = 100
> UNTIL count = 4 OR iterations = 20
>
> i do something like this:
>
> iterations = 0
> count = 0
>
> m_Switch = (1,10,100)
>
> while True:
> iterations +=1
> ...
> if (genericCondition):
> count +=1
> ...
> try:
> m = m_Switch[count-1]
> except: pass
> if count = 4 or iterations = 20
>
> the problem is that when count = 4 m_Switch[4-1] have no value, so i use
> the try..except.
>
> Is there a better solution to solve this problem? and, generally
> speaking, the try..except block slow down the execution of the program or
> not?
>
Use a dict:

m_Switch = {1: 1, 2: 10, 3: 100}

and then catch the KeyError.

Don't use a bare 'except', catch the specific exception you want to
catch, and don't worry about the speed unless you discover that it's
real problem.

Gregory Ewing

3/3/2010 6:23:00 AM

0

Alf P. Steinbach wrote:
> * Tracubik:
>
>> iterations=0;
>> count=0;
>> REPEAT;
>> iterations = iterations+1;
>> ...
>> IF (genericCondition) THEN count=count+1;
>> ...
>> CASE count OF:
>> 1: m = 1
>> 2: m = 10
>> 3: m = 100
>
> Uhm, is this syntactically valid Pascal? As I recall, every Pascal
> construct was delimited in some way.

I think it's okay. Pascal's control structures such as
if-then and while-do mostly take single statements and
didn't have an ending keyword. If you want multiple
statements in the body you have to put begin-end around
them.

Putting a semicolon after REPEAT is stylistically a
bit odd, but it's not wrong.

--
Greg

Andre Engels

3/3/2010 8:10:00 AM

0

On Tue, Mar 2, 2010 at 6:46 PM, Tracubik <affdfsdfdsfsd@b.com> wrote:

> and, generally
> speaking, the try..except block slow down the execution of the program or
> not?

Try...except tends to be slow when the exception does occur, fast when
it does not. Apart from that, if these
fraction-of-a-fraction-of-a-second gains are important to you, Python
is not the programming language for you.

In Python, it seems to be common to do optimization after rather than
during the main coding, and then only when it is necessary and only
where it matters. That is:
1. Program your solution without looking much at speed issues
2. Check if it is fast enough. If so, ready.
3. If not, see which parts of the program are being slow
4. Optimize only those parts of the program that have been identified in step 3

--
André Engels, andreengels@gmail.com

Peter Otten

3/3/2010 8:40:00 AM

0

Tracubik wrote:

> hi, i've to convert from Pascal this code:

program loop;

function generic_condition: boolean;
begin
generic_condition := random > 0.7
end;

procedure loop;
var
iterations, count, m: integer;
begin
iterations := 0;
count := 0;
m := 0;
repeat
iterations := iterations+1;
(*...*)
writeln(iterations:2, count:2, m:4);
(*...*)
if generic_condition then
inc(count);
(*...*)
case count of
1: m := 1;
2: m := 10;
3: m := 100
end
until (count = 4) or (iterations = 20)
end;

begin
loop;
writeln("That's all, folks")
end.

Hey, I have a Pascal compiler just one apt-get away ;)

Here's how I'd translate the above, without trying to be too clever:

from random import random

def generic_condition():
return random() > 0.7

def loop():
count = 0
m = 0
lookup = {1: 1, 2: 10, 3: 100}
for iterations in range(20): # off by one
# ...
print "%2d %1d %3d" % (iterations, count, m)
# ...
if generic_condition():
count += 1
# ...
m = lookup.get(count, m)
if count == 4:
break

if __name__ == "__main__":
loop()
print "That's all, folks"

Something must be wrong with me today because I find the Pascal code /more/
readable...

Peter

MRAB

3/3/2010 2:45:00 PM

0

Gregory Ewing wrote:
> Alf P. Steinbach wrote:
>> * Tracubik:
> >
>>> iterations=0;
>>> count=0;
>>> REPEAT;
>>> iterations = iterations+1;
>>> ...
>>> IF (genericCondition) THEN count=count+1;
>>> ...
>>> CASE count OF:
>>> 1: m = 1
>>> 2: m = 10
>>> 3: m = 100
>>
>> Uhm, is this syntactically valid Pascal? As I recall, every Pascal
>> construct was delimited in some way.
>
> I think it's okay. Pascal's control structures such as
> if-then and while-do mostly take single statements and
> didn't have an ending keyword. If you want multiple
> statements in the body you have to put begin-end around
> them.
>
> Putting a semicolon after REPEAT is stylistically a
> bit odd, but it's not wrong.
>
There shouldn't be a colon after the 'OF', and the cases themselves
should be separated by semicolons (the case-statement itself ends with
'end').

Tracubik

3/3/2010 5:38:00 PM

0

Il Wed, 03 Mar 2010 09:39:54 +0100, Peter Otten ha scritto:

> Tracubik wrote:
>
>> hi, i've to convert from Pascal this code:
>
> program loop;
>
> function generic_condition: boolean;
> begin
> generic_condition := random > 0.7
> end;
>
> procedure loop;
> var
> iterations, count, m: integer;
> begin
> iterations := 0;
> count := 0;
> m := 0;
> repeat
> iterations := iterations+1;
> (*...*)
> writeln(iterations:2, count:2, m:4);
> (*...*)
> if generic_condition then
> inc(count);
> (*...*)
> case count of
> 1: m := 1;
> 2: m := 10;
> 3: m := 100
> end
> until (count = 4) or (iterations = 20)
> end;
>
> begin
> loop;
> writeln("That's all, folks")
> end.
>
> Hey, I have a Pascal compiler just one apt-get away ;)
>
> Here's how I'd translate the above, without trying to be too clever:
>
> from random import random
>
> def generic_condition():
> return random() > 0.7
>
> def loop():
> count = 0
> m = 0
> lookup = {1: 1, 2: 10, 3: 100}
> for iterations in range(20): # off by one
> # ...
> print "%2d %1d %3d" % (iterations, count, m) # ...
> if generic_condition():
> count += 1
> # ...
> m = lookup.get(count, m)
> if count == 4:
> break
>
> if __name__ == "__main__":
> loop()
> print "That's all, folks"
>
> Something must be wrong with me today because I find the Pascal code
> /more/ readable..

i was think the same, Pascal seem to generate a great more readable code.
I'm a newbie, so my opinion is probably wrong, but i still think that
don't have CASE OF and REPEAT UNTIL code block return in difficult-to-
read code.

>
> Peter

Nico