loops

[Gandalf]

how can I do width python a normal for loop width tree conditions like
for example :

for x=1;x<=100;x+x:
print x


thanks

[Duncan Booth]

Re: loops

Gandalf <goldnery@gmail .comwrote:

how can I do width python a normal for loop width tree conditions like
for example :
>
for x=1;x<=100;x+x:
print x
>

What you wrote would appear to be an infinite loop so I'll assume you meant
to assign something to x each time round the loop as well. The simple
Python translation of what I think you meant would be:

x = 1
while x <= 100:
print x
x += x

If you really insist on doing it with a for loop:

def doubling(start, limit):
x = start
while x <= limit:
yield x
x += x

....

for x in doubling(1, 100):
print x

[Gandalf]

Re: loops

On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

Gandalf <goldn...@gmail .comwrote:

how can I do width python a normal for loop width tree conditions like
for example :

>

for x=1;x<=100;x+x:
    print x

>
What you wrote would appear to be an infinite loop so I'll assume you meant
to assign something to x each time round the loop as well. The simple
Python translation of what I think you meant would be:
>
x = 1
while x <= 100:
   print x
   x += x
>
If you really insist on doing it with a for loop:
>
def doubling(start, limit):
    x = start
    while x <= limit:
        yield x
        x += x
>
...
>
for x in doubling(1, 100):
    print x

thanks

[Gandalf]

Re: loops

On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

Gandalf <goldn...@gmail .comwrote:

how can I do width python a normal for loop width tree conditions like
for example :

>

for x=1;x<=100;x+x:
    print x

>
What you wrote would appear to be an infinite loop so I'll assume you meant
to assign something to x each time round the loop as well. The simple
Python translation of what I think you meant would be:
>
x = 1
while x <= 100:
   print x
   x += x
>
If you really insist on doing it with a for loop:
>
def doubling(start, limit):
    x = start
    while x <= limit:
        yield x
        x += x
>
...
>
for x in doubling(1, 100):
    print x

I was hopping to describe it with only one command. most of the
languages I know use this.
It seems weird to me their is no such thing in python. it's not that I
can't fined a solution it's all about saving code

[robert]

Re: loops

Gandalf wrote:

On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

>Gandalf <goldn...@gmail .comwrote:

>>how can I do width python a normal for loop width tree conditions like
>>for example :
>>for x=1;x<=100;x+x:
>> print x

>What you wrote would appear to be an infinite loop so I'll assume you meant
>to assign something to x each time round the loop as well. The simple
>Python translation of what I think you meant would be:
>>
>x = 1
>while x <= 100:
> print x
> x += x
>>

...

>
I was hopping to describe it with only one command. most of the
languages I know use this.
It seems weird to me their is no such thing in python. it's not that I
can't fined a solution it's all about saving code

You'd not save code, but only lines (and clearness). You'd also
need more (non-space) characters

Python saves confusion and arbitrariness =you'll usually code
faster, because you don't think so much about voluptuous
multimulti..pos sibilites, not worth the play: one-ness of mind

If insistent, you could sometimes save lines like this ;-)

x=1
while x<=100: print x; x+=x


Robert

[Aaron Brady]

Re: loops

Gandalf wrote:

On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

>Gandalf <goldn...@gmail .comwrote:

how can I do width python a normal for loop width tree conditions like
for example :

>>

for x=1;x<=100;x+x:
    print x

>>
>What you wrote would appear to be an infinite loop so I'll assume you meant
>to assign something to x each time round the loop as well. The simple
>Python translation of what I think you meant would be:
>>
>x = 1
>while x <= 100:
>   print x
>   x += x
>>
>If you really insist on doing it with a for loop:
>>
>def doubling(start, limit):
>    x = start
>    while x <= limit:
>        yield x
>        x += x
>>
>...
>>
>for x in doubling(1, 100):
>    print x

>
I was hopping to describe it with only one command. most of the
languages I know use this.
It seems weird to me their is no such thing in python. it's not that I
can't fined a solution it's all about saving code

Do you anticipate reusing it? You could make something a little more
extendable.

for x in iexpression( 'x', 1, 100, 'x+x' ):
print x

or

for x in iexpression( lambda x: x+x, 1, 100 ):
print x

I'm assuming you don't want or have a closed form, in this case x= 2**
_x.

[Terry Reedy]

Re: loops

Gandalf wrote:

On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

>Gandalf <goldn...@gmail .comwrote:

>>how can I do width python a normal for loop width tree conditions like
>>for example :
>>for x=1;x<=100;x+x:
>> print x

>What you wrote would appear to be an infinite loop so I'll assume you meant
>to assign something to x each time round the loop as well. The simple
>Python translation of what I think you meant would be:
>>
>x = 1
>while x <= 100:
> print x
> x += x
>>
>If you really insist on doing it with a for loop:
>>
>def doubling(start, limit):
> x = start
> while x <= limit:
> yield x
> x += x
>>
>...
>>
>for x in doubling(1, 100):
> print x

>
I was hopping to describe it with only one command. most of the
languages I know use this.
It seems weird to me their is no such thing in python. it's not that I
can't fined a solution it's all about saving code

Python: 'makes common things easy and uncommon things possible'.

The large majority of use cases for iteration are iterating though
sequences, actual and virtual, including integers with a constant step
size. Python make that trivial to do and clear to read. Your example is
trivially written as

for i in range(11):
print 2**i

Python provide while loops for more fine-grain control, and a protocol
so *reuseable* iterators can plug into for loops. Duncan showed you
both. If you *need* a doubling loop variable once, you probably need
one more than once, and the cost of the doubling generator is amortized
over all such uses. Any Python proprammer should definitely know how to
write such a thing without hardly thinking. We can squeeze a line out
of this particular example:

def doubling(value, limit):
while value <= limit:
yield value
value += value

Terry Jan Reedy

[wbowers]

Re: loops

On Oct 18, 11:31 am, Terry Reedy <tjre...@udel.e duwrote:

Gandalf wrote:

On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

Gandalf <goldn...@gmail .comwrote:
>how can I do width python a normal for loop width tree conditions like
>for example :
>for x=1;x<=100;x+x:
>    print x
What you wrote would appear to be an infinite loop so I'll assume you meant
to assign something to x each time round the loop as well. The simple
Python translation of what I think you meant would be:

>

x = 1
while x <= 100:
   print x
   x += x

>

If you really insist on doing it with a for loop:

>

def doubling(start, limit):
    x = start
    while x <= limit:
        yield x
        x += x

>

...

>

for x in doubling(1, 100):
    print x

>

I was hopping to describe it with only one command. most of the
languages I know use this.
It seems weird to me their is no such thing in python. it's not that I
can't fined a solution it's all about saving code

>
Python: 'makes common things easy and uncommon things possible'.
>
The large majority of use cases for iteration are iterating though
sequences, actual and virtual, including integers with a constant step
size.  Python make that trivial to do and clear to read. Your example is
trivially written as
>
for i in range(11):
   print 2**i
>
Python provide while loops for more fine-grain control, and a protocol
so *reuseable* iterators can plug into for loops. Duncan showed you
both.  If you *need* a doubling loop variable once, you probably need
one more than once, and the cost of the doubling generator is amortized
over all such uses.  Any Python proprammer should definitely know how to
write such a thing without hardly thinking.  We can squeeze a line out
of this particular example:
>
def doubling(value, limit):
   while value <= limit:
     yield value
     value += value
>
Terry Jan Reedy

I agree that using range() for simple iterations is the way to go.
Here are some examples of python expressions you'd use in specific
situations:

# instead of for (i = 0; i < 100; i++)
for i in range(100): pass

# instead of for (i = 10; i < 100; i++)
for i in range(10, 100): pass

# instead of for (i = 1; i < 100; i += 2)
for i in range(1, 100, 2): pass

# instead of for (i = 99; i >= 0; i--)
for i in range(100)[::-1]: pass

There's always a way to do it, and it's almost always really simple :-D

[Duncan Booth]

Re: loops

wbowers <william.bowers @gmail.comwrote :

I agree that using range() for simple iterations is the way to go.

except that as Terry said, "The large majority of use cases for iteration
are iterating though sequences"

I very rarely use range() in iterations.

Here are some examples of python expressions you'd use in specific
situations:
>

....

# instead of for (i = 99; i >= 0; i--)
for i in range(100)[::-1]: pass

or:
for i in xrange(99, -1, -1): pass

[robert]

Re: loops

Aaron Brady wrote:

Gandalf wrote:
>

>On Oct 18, 12:39 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
>wrote:

>>Gandalf <goldn...@gmail .comwrote:
>>>how can I do width python a normal for loop width tree conditions like
>>>for example :
>>>for x=1;x<=100;x+x:
>>> print x
>>What you wrote would appear to be an infinite loop so I'll assume you meant
>>to assign something to x each time round the loop as well. The simple
>>Python translation of what I think you meant would be:
>>>
>>x = 1
>>while x <= 100:
>> print x
>> x += x
>>>
>>If you really insist on doing it with a for loop:
>>>
>>def doubling(start, limit):
>> x = start
>> while x <= limit:
>> yield x
>> x += x
>>>
>>...
>>>
>>for x in doubling(1, 100):
>> print x

>I was hopping to describe it with only one command. most of the
>languages I know use this.
>It seems weird to me their is no such thing in python. it's not that I
>can't fined a solution it's all about saving code

>
Do you anticipate reusing it? You could make something a little more
extendable.
>
for x in iexpression( 'x', 1, 100, 'x+x' ):
print x
>
or
>
for x in iexpression( lambda x: x+x, 1, 100 ):
print x
>
I'm assuming you don't want or have a closed form, in this case x= 2**
_x.
>

#and to learn even more about this, import this:
import this # ;-)

[Steven D'Aprano]

Re: loops

On Sat, 18 Oct 2008 03:52:51 -0700, Gandalf wrote:

I was hopping to describe it with only one command. most of the
languages I know use this.
It seems weird to me their is no such thing in python. it's not that I
can't fined a solution it's all about saving code

It shouldn't be about saving code. There's no shortage of code so that we
have to conserve it. But there is a shortage of time and effort, so
making your code easy to read and easy to maintain is far more important.

for x in (2**i for i in xrange(10)):
print x

will also print 1, 2, 4, 8, ... up to 1000.



--
Steven

[James Mills]

Re: loops

On Sun, Oct 19, 2008 at 1:30 PM, Steven D'Aprano
<steve@remove-this-cybersource.com .auwrote:

for x in (2**i for i in xrange(10)):
print x

This is by far the most concise solution I've seen so far.
And it should never be about conserving code.
Also, Python IS NOT C (to be more specific: Python
is not a C-class language).

--JamesMills

--
--
-- "Problems are solved by method"

[John Machin]

Re: loops

On Oct 19, 2:30 pm, Steven D'Aprano <st...@REMOVE-THIS-
cybersource.com .auwrote:
[snip]

making your code easy to read and easy to maintain is far more important.
>
for x in (2**i for i in xrange(10)):
    print x
>
will also print 1, 2, 4, 8, ... up to 1000.

I would say up to 512; perhaps your understanding of "up to" differs
from mine.

Easy to read? I'd suggest this:

for i in xrange(10):
print 2 ** i

Cheers,
John

[James Mills]

Re: loops

On Sun, Oct 19, 2008 at 1:44 PM, James Mills
<prologic@short circuit.net.auw rote:

On Sun, Oct 19, 2008 at 1:30 PM, Steven D'Aprano
<steve@remove-this-cybersource.com .auwrote:

>for x in (2**i for i in xrange(10)):
> print x

>
This is by far the most concise solution I've seen so far.
And it should never be about conserving code.
Also, Python IS NOT C (to be more specific: Python
is not a C-class language).

Also, if the OP is finding himself writing such manual
and mundane looking loops, he/she should reconsider
what it is he/she is doing. You would normally want
to iterate (vs. loop) over a sequence of items.

--JamesMills

--
--
-- "Problems are solved by method"

[Paul Rubin]

Re: loops

"James Mills" <prologic@short circuit.net.auw rites:

for x in (2**i for i in xrange(10)):
print x

This is by far the most concise solution I've seen so far.

print '\n'.join(str(2 **i) for i in xrange(10))