Re: How to test if object is an integer?
On Mon, 17 Oct 2011 18:59:44 -0600, Ian Kelly wrote:
> On Mon, Oct 17, 2011 at 6:40 PM, Chris Kaynor
> wrote:
>> Python 2.6 running on Windows 7:
> 99.0**99**99
>> OverflowError: (34, 'Result too large') Traceback (most recent call
>> last):
>> File "", line 1, in
>> OverflowError: (34, 'Result too large')
>>
>> However, from the documentation:
>> "Because of the lack of standardization of floating point exception
>> handling in C, most floating point operations also aren’t checked."
>> (http://docs.python.org/library/
exceptions.html#exceptions.OverflowError)
>
> I think what Roy meant was "can you even get an OverflowError from
> calling int() any more", to which I think the answer is no, since in
> modern Pythons int() will auto-promote to a long, and in Python 3
> they're even the same thing.
You can still get an OverflowError:
>>> inf = float('inf')
>>> int(inf)
Traceback (most recent call last):
File "", line 1, in
OverflowError: cannot convert float infinity to integer
and similarly for Decimal('inf') as well.
--
Steven
--
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Re: How to test if object is an integer?
- Original Message - > From: Noah Hall > To: MrPink > Cc: python-list@python.org > Sent: Tuesday, October 18, 2011 4:44 AM > Subject: Re: How to test if object is an integer? > There's the isdigit method, for example - > >>>> str = "1324325" >>>> str.isdigit() > True >>>> str = "1232.34" >>>> str.isdigit() > False >>>> str = "I am a string, not an int!" >>>> str.isdigit() > False > There are some corner cases to be considered with this approach: 1. negative integers: '-3' 2. strings starting with '0': '03' 3. strings starting with one '+': '+3' -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On Mon, Oct 17, 2011 at 6:40 PM, Chris Kaynor wrote: > Python 2.6 running on Windows 7: 99.0**99**99 > OverflowError: (34, 'Result too large') > Traceback (most recent call last): > File "", line 1, in > OverflowError: (34, 'Result too large') > > However, from the documentation: > "Because of the lack of standardization of floating point exception > handling in C, most floating point operations also aren’t checked." > (http://docs.python.org/library/exceptions.html#exceptions.OverflowError) I think what Roy meant was "can you even get an OverflowError from calling int() any more", to which I think the answer is no, since in modern Pythons int() will auto-promote to a long, and in Python 3 they're even the same thing. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
Python 2.6 running on Windows 7:
>>> 99.0**99**99
OverflowError: (34, 'Result too large')
Traceback (most recent call last):
File "", line 1, in
OverflowError: (34, 'Result too large')
However, from the documentation:
"Because of the lack of standardization of floating point exception
handling in C, most floating point operations also aren’t checked."
(http://docs.python.org/library/exceptions.html#exceptions.OverflowError)
Chris
On Mon, Oct 17, 2011 at 5:33 PM, Roy Smith wrote:
>
> In article ,
> Mathias Lafeldt wrote:
>
> > According to [1], there're more Exceptions to test for:
> >
> > try:
> > int(s)
> > return True
> > except (TypeError, ValueError, OverflowError): # int conversion failed
> > return False
>
>
> I don't think I would catch TypeError here. It kind of depends on how
> isInt() is defined. Is it:
>
> def isInt(s):
> "Return True if s is a string representing an integer"
>
> or is it:
>
> def isInt(s):
> "Return True if s (which must be a string) represents an integer"
>
> If the latter, then passing a non-string violates the contract, and the
> function should raise TypeError. If the former, then you could make
> some argument for catching the TypeError and returning False, but I
> think the second version is what most people have in mind for isInt().
>
> Can you even get an OverflowError any more in a modern Python?
>
> >>>
> int('9')
> 9L
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Re: How to test if object is an integer?
In article ,
Mathias Lafeldt wrote:
> According to [1], there're more Exceptions to test for:
>
> try:
> int(s)
> return True
> except (TypeError, ValueError, OverflowError): # int conversion failed
> return False
I don't think I would catch TypeError here. It kind of depends on how
isInt() is defined. Is it:
def isInt(s):
"Return True if s is a string representing an integer"
or is it:
def isInt(s):
"Return True if s (which must be a string) represents an integer"
If the latter, then passing a non-string violates the contract, and the
function should raise TypeError. If the former, then you could make
some argument for catching the TypeError and returning False, but I
think the second version is what most people have in mind for isInt().
Can you even get an OverflowError any more in a modern Python?
>>>
int('9')
9L
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Re: How to test if object is an integer?
On Mon, Oct 17, 2011 at 2:44 PM, Noah Hall wrote: > There's the isdigit method, for example - > str = "1324325" str.isdigit() > True str = "1232.34" str.isdigit() > False str = "I am a string, not an int!" str.isdigit() > False That works for non-negative base-10 integers. But: >>> "-1234".isdigit() False Cheers, Ian -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On Sat, Oct 15, 2011 at 12:44 AM, MrPink wrote: > > Is there a function in Python that can be used to test if the value in > a string is an integer? I had to make one up for myself and it looks > like this: > > def isInt(s): > try: > i = int(s) > return True > except ValueError: > return False There's the isdigit method, for example - >>> str = "1324325" >>> str.isdigit() True >>> str = "1232.34" >>> str.isdigit() False >>> str = "I am a string, not an int!" >>> str.isdigit() False -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On Sat, Oct 15, 2011 at 1:44 AM, MrPink wrote: > > Is there a function in Python that can be used to test if the value in > a string is an integer? I had to make one up for myself and it looks > like this: > > def isInt(s): > try: > i = int(s) > return True > except ValueError: > return False According to [1], there're more Exceptions to test for: try: int(s) return True except (TypeError, ValueError, OverflowError): # int conversion failed return False [1] http://jaynes.colorado.edu/PythonIdioms.html, idiom "Catch errors rather than avoiding them to avoid cluttering your code with special cases" -Mathias -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On 10/14/2011 9:51 PM, Ben Finney wrote: Terry Reedy writes: On 10/14/2011 9:05 PM, Chris Angelico wrote: That tests if the object is already an int; the OP asked if a string contains an integer. The misleading subject line did not. It should have been "How to test if a string contains an integer?" Which would still be misleading :-) Even better is “How to test whether a string is a valid representation of an integer?” I agree, but that is more than I would ask of a newbie, whereas asking people to ask the same question in subject line and text, even if the question is inadequate, is reasonable. I say that's better because it gets to the relevant point of asking *which* representations you want to test for – what qualifies as valid for your particular use case, and what does not. There's no single right answer; the programmer must choose exactly what they want to test for. Yes. Even the wrong subject line question is ambiguous, as any of int, bool, float, complex, decimal.Decimal, and fractions.Fraction can have an integer value, as might user class instances, and, of course, depending on context, bytes and strings. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
Terry Reedy writes: > On 10/14/2011 9:05 PM, Chris Angelico wrote: > > That tests if the object is already an int; the OP asked if a string > > contains an integer. > > The misleading subject line did not. It should have been "How to test > if a string contains an integer?" Which would still be misleading :-) Even better is “How to test whether a string is a valid representation of an integer?” I say that's better because it gets to the relevant point of asking *which* representations you want to test for – what qualifies as valid for your particular use case, and what does not. There's no single right answer; the programmer must choose exactly what they want to test for. -- \ “When I was a little kid we had a sand box. It was a quicksand | `\ box. I was an only child... eventually.” —Steven Wright | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On 10/14/2011 9:05 PM, Chris Angelico wrote: 2011/10/15 惜悯: retrun True if type(i) is int else False That tests if the object is already an int; the OP asked if a string contains an integer. The misleading subject line did not. It should have been "How to test if a string contains an integer?" -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On Fri, Oct 14, 2011 at 6:05 PM, Chris Angelico wrote: > 2011/10/15 惜悯 : >> retrun True if type(i) is int else False > > That tests if the object is already an int; the OP asked if a string > contains an integer. Additionally: * the if-then-else there is unnecessary since `type(i) is int` already returns a bool * such a type test is normally and better written `isinstance(i, int)` Cheers, Chris R. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
2011/10/15 惜悯 : > retrun True if type(i) is int else False That tests if the object is already an int; the OP asked if a string contains an integer. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
retrun True if type(i) is int else False -- Original -- From: "Chris Angelico"; Date: Sat, Oct 15, 2011 08:55 AM To: "python-list"; Subject: Re: How to test if object is an integer? On Sat, Oct 15, 2011 at 10:44 AM, MrPink wrote: > Is there a function in Python that can be used to test if the value in > a string is an integer? I had to make one up for myself and it looks > like this: > > def isInt(s): >try: >i = int(s) >return True >except ValueError: >return False There's some ambiguity in the definition of "is an integer". For instance, is "0x100" an integer? Is "0800"? If your definition of "is an integer" is "can be passed to int() without triggering an exception" (which is probably the most useful), then your above code is about perfect. The only change I'd make is to not have an isInt function at all, but simply to try/except at the point where you need to make the conversion. ChrisA -- http://mail.python.org/mailman/listinfo/python-list-- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if object is an integer?
On Sat, Oct 15, 2011 at 10:44 AM, MrPink wrote: > Is there a function in Python that can be used to test if the value in > a string is an integer? I had to make one up for myself and it looks > like this: > > def isInt(s): > try: > i = int(s) > return True > except ValueError: > return False There's some ambiguity in the definition of "is an integer". For instance, is "0x100" an integer? Is "0800"? If your definition of "is an integer" is "can be passed to int() without triggering an exception" (which is probably the most useful), then your above code is about perfect. The only change I'd make is to not have an isInt function at all, but simply to try/except at the point where you need to make the conversion. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
How to test if object is an integer?
Is there a function in Python that can be used to test if the value in a string is an integer? I had to make one up for myself and it looks like this: def isInt(s): try: i = int(s) return True except ValueError: return False -- http://mail.python.org/mailman/listinfo/python-list
