Re: how to check if a value is a floating point or not
Guys i am only a beginner at python most of the stuff you are saying i need to do i dont understand. -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On Fri, Jun 20, 2014 at 12:14 AM, Nicholas Cannon nicholascann...@gmail.com wrote: Guys i am only a beginner at python most of the stuff you are saying i need to do i dont understand. All we're saying is that the simplest and most accurate way to determine whether a string can be converted to an int or a float is to try converting it and see if it succeeds. If it fails, it will raise an exception that you can catch using the try-except syntax. Here's what your checkint function might look like: def checkint(a): try: int(a) except ValueError: return False else: return True -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
Nicholas Cannon nicholascann...@gmail.com wrote: Guys i am only a beginner at python most of the stuff you are saying i need to do i dont understand. Then listen and try to learn :-) In C it is customary to do all sorts of sanity checks in advance. Validating user input is an example. We can call this to ask permission. This coding style is often neccessary in C, but not recommended in Python. In Python we just try to do what we want. If it fails, we get an exception, e.g. a ValueError. Then we do something with this error instead. We can call this to ask forgiveness. If you think you need a validator, you are very likely thinking unpythonic. Thus, we don't have to check that the user typed in a float. We just try to construct a float from the input. If it fails it wasn't convertible to a float. But you don't have to know that in advance. All the checks you need to do is already in the function float(). You don't have to repeat them. float() will succeed or raise an error. Same for conversion to int: If the user input is convertible to int, the function int() will do that. If it's not convertible, you get an exception. Just trap the exception and deal with it when it occurs. But don't use try/except everywhere! Some exceptions might be due to an error in your own code, i.e. not in the user input. Those errors you should not silence, but let your program crash and abort. Then you will know there is an error in your code. That is what an unhandled exception will do, and in addition it will tell you where the error is and what it is, so just leave those exceptions unhandled. Sturla -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On 20/06/2014 14:16, Sturla Molden wrote: Nicholas Cannon nicholascann...@gmail.com wrote: Guys i am only a beginner at python most of the stuff you are saying i need to do i dont understand. Then listen and try to learn :-) But don't use try/except everywhere! Some exceptions might be due to an error in your own code, i.e. not in the user input. Those errors you should not silence, but let your program crash and abort. Then you will know there is an error in your code. That is what an unhandled exception will do, and in addition it will tell you where the error is and what it is, so just leave those exceptions unhandled. For the OP a very important rule of thumb is never use a bare except, so this is right out. try: doSomething() except: WTF() -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On 2014-06-20, Mark Lawrence breamore...@yahoo.co.uk wrote: For the OP a very important rule of thumb is never use a bare except, so this is right out. try: doSomething() except: WTF() IMO, that sort of depends on WTF() does. One case where a bare except is well used is when stdandard output/error are not going anywhere useful and you want to log the exception and then terminate: try: whatever() except Exception as e: syslog(foobar: terminating due to unhandled exception %s.\n % e) sys.exit(1) Alternatively, if you're not at the top level in the call tree, sometimes it's useful to log an exception but still pass it on up in case somebody higher up wants to handle it: def asdf(): try: whatever() except Exception as e: syslog(Function asdf() terminating due to exception %s.\n % e) raise -- Grant Edwards grant.b.edwardsYow! ... or were you at driving the PONTIAC that gmail.comHONKED at me in MIAMI last Tuesday? -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On Fri, 20 Jun 2014 14:28:52 +, Grant Edwards wrote: On 2014-06-20, Mark Lawrence breamore...@yahoo.co.uk wrote: For the OP a very important rule of thumb is never use a bare except, so this is right out. try: doSomething() except: WTF() IMO, that sort of depends on WTF() does. One case where a bare except is well used is when stdandard output/error are not going anywhere useful and you want to log the exception and then terminate: try: whatever() except Exception as e: syslog(foobar: terminating due to unhandled exception %s.\n % e) sys.exit(1) Alternatively, if you're not at the top level in the call tree, sometimes it's useful to log an exception but still pass it on up in case somebody higher up wants to handle it: def asdf(): try: whatever() except Exception as e: syslog(Function asdf() terminating due to exception %s.\n % e) raise I think that is getting beyond the level of the O.P. All guide lines may have exceptions but until you have developed enough to realise where they can be safely ignored it is best to follow them. -- I was in Vegas last week. I was at the roulette table, having a lengthy argument about what I considered an Odd number. -- Steven Wright -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On Fri, Jun 20, 2014 at 8:28 AM, Grant Edwards invalid@invalid.invalid wrote: On 2014-06-20, Mark Lawrence breamore...@yahoo.co.uk wrote: For the OP a very important rule of thumb is never use a bare except, so this is right out. try: doSomething() except: WTF() IMO, that sort of depends on WTF() does. One case where a bare except is well used is when stdandard output/error are not going anywhere useful and you want to log the exception and then terminate: try: whatever() except Exception as e: syslog(foobar: terminating due to unhandled exception %s.\n % e) sys.exit(1) Logging unhandled exceptions and exiting is the job of sys.excepthook, so I would prefer to replace it with a custom exception handler in this case. Also, this isn't an example of a bare except, which is an except clause with no exception class specified. except: and except Exception: are not equivalent. In Python 3, I believe that except: and except BaseException: are equivalent. In Python 2 they are not, because exceptions are also allowed to be old-style classes. In any case, the advice against bare excepts stems from the fact that bare excepts will catch things that you usually should not try to catch, such as SystemExit and KeyboardInterrupt, and so you should normally specify except Exception: in the most general case. -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On 06/18/2014 10:53 PM, nicholascann...@gmail.com wrote: I am making a calculator and i need it to support floating point values but i am using the function isnumeric to check if the user has entered an int value. I need the same for floating point types so i could implement an or in the if statement that checks the values the user has entered and allow it to check and use floating points. If you need the source code i am happy to give it to you. Thank you for your help Your mention of *isnumeric* indicates to me that you are using Python3 (correct?) and are wishing to test if a *string* contains characters that represent an int or a float (correct?). The easiest way to test such is to just try to convert it to an int or float, and catch failures as an indication that it is not valid. Something like: try: value = float(s) except ValueError: ... handle invalid string ... Gary Herron -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On Thursday, June 19, 2014 1:53:31 PM UTC+8, Nicholas Cannon wrote: I am making a calculator and i need it to support floating point values but i am using the function isnumeric to check if the user has entered an int value. I need the same for floating point types so i could implement an or in the if statement that checks the values the user has entered and allow it to check and use floating points. If you need the source code i am happy to give it to you. Thank you for your help I am using python 2.7.7 and i have come up with away but there is still possible errors for this. What i did was i this #checks if the user input is an integer value def checkint(a): if a.isnumeric(): return True else: if a.isalpha(): return False else: return True The parameter a is the users input by the raw_input function. I first test if it is normal int with the isnumeric function. Unfortunately this function picks up the decimal as false. This means if the user inputs a float it has to be false. I then test if this input has any alphabetical characters if it does not the user could have only entered something like 12.5 oppose to abc.d. This method works fine and it i have tested it and it works fine. if incase this input did have a letter it would be picked up by the isalpha function. There is one annoying error doing it this way and that is if you enter 12.ab or ab.12 it will say that it is okay. Still working on this so this should get sorted out soon. -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
Nicholas Cannon nicholascann...@gmail.com writes: #checks if the user input is an integer value def checkint(a): if a.isnumeric(): return True else: if a.isalpha(): return False else: return True What code will be using this function? Why would that not be better replaced with a ‘try … except’ construction? That is, don't do this (Look Before You Leap):: foo = get_a_string() if checkint(foo): bar = int(foo) else: bar = None Instead, do this (Easier to Ask Forgiveness than Permission):: foo = get_a_string() try: bar = int(foo) except ValueError: bar = None If you need to create an integer based on a string, just do it, and handle the exception (if any) at an appropriate level. There is one annoying error doing it this way and that is if you enter 12.ab or ab.12 it will say that it is okay. Still working on this so this should get sorted out soon. You are re-inventing a wheel (the ‘int’ callable) which already does all of that properly. Make use of it, and your frustration will be reduced. -- \ “It is far better to grasp the universe as it really is than to | `\persist in delusion, however satisfying and reassuring.” —Carl | _o__)Sagan | Ben Finney -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On Thu, Jun 19, 2014 at 12:48 AM, Nicholas Cannon nicholascann...@gmail.com wrote: On Thursday, June 19, 2014 1:53:31 PM UTC+8, Nicholas Cannon wrote: I am making a calculator and i need it to support floating point values but i am using the function isnumeric to check if the user has entered an int value. I need the same for floating point types so i could implement an or in the if statement that checks the values the user has entered and allow it to check and use floating points. If you need the source code i am happy to give it to you. Thank you for your help I am using python 2.7.7 and i have come up with away but there is still possible errors for this. What i did was i this #checks if the user input is an integer value def checkint(a): if a.isnumeric(): return True else: if a.isalpha(): return False else: return True The parameter a is the users input by the raw_input function. I first test if it is normal int with the isnumeric function. Unfortunately this function picks up the decimal as false. This means if the user inputs a float it has to be false. I then test if this input has any alphabetical characters if it does not the user could have only entered something like 12.5 oppose to abc.d. unicode.isalpha does not test if the input has *any* alphabetic characters. It tests if the input is *only* alphabetic characters. u'12.5'.isalpha() does return False. u'abc.d'.isalpha() *also* returns False, because the decimal point is not alphabetic. I second Gary Herron's suggestion to just try converting the value and catch the exception if it fails. Python already knows how to do this for you; there's no need to reinvent the wheel. -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
On Thu, Jun 19, 2014 at 1:23 AM, Ian Kelly ian.g.ke...@gmail.com wrote: On Thu, Jun 19, 2014 at 12:48 AM, Nicholas Cannon nicholascann...@gmail.com wrote: On Thursday, June 19, 2014 1:53:31 PM UTC+8, Nicholas Cannon wrote: I am making a calculator and i need it to support floating point values but i am using the function isnumeric to check if the user has entered an int value. I need the same for floating point types so i could implement an or in the if statement that checks the values the user has entered and allow it to check and use floating points. If you need the source code i am happy to give it to you. Thank you for your help I am using python 2.7.7 and i have come up with away but there is still possible errors for this. What i did was i this #checks if the user input is an integer value def checkint(a): if a.isnumeric(): return True else: if a.isalpha(): return False else: return True The parameter a is the users input by the raw_input function. I first test if it is normal int with the isnumeric function. Unfortunately this function picks up the decimal as false. This means if the user inputs a float it has to be false. I then test if this input has any alphabetical characters if it does not the user could have only entered something like 12.5 oppose to abc.d. unicode.isalpha does not test if the input has *any* alphabetic characters. It tests if the input is *only* alphabetic characters. u'12.5'.isalpha() does return False. u'abc.d'.isalpha() *also* returns False, because the decimal point is not alphabetic. Incidentally, unicode.isnumeric is probably not what you want either. According to the docs, it returns True if there are only numeric characters in S, False otherwise. Numeric characters include digit characters, and all characters that have the Unicode numeric value property, e.g. U+2155, VULGAR FRACTION ONE FIFTH. So that includes strings like u'123⅕⅓Ⅷ٤', which is clearly not an integer. You'd likely do better with unicode.isdigit, and even then you'd be allowing for mixed scripts. -- https://mail.python.org/mailman/listinfo/python-list
Re: how to check if a value is a floating point or not
nicholascann...@gmail.com wrote: I am making a calculator and i need it to support floating point values but i am using the function isnumeric to check if the user has entered an int value. I need the same for floating point types so i could implement an or in the if statement that checks the values the user has entered and allow it to check and use floating points. If you need the source code i am happy to give it to you. Thank you for your help It's better to ask forgiveness than ask permission... You don't have to check anything. If the user enters something that cannot be coverted to a float, the function float() will raise an exception: try: x = float(value) except ValueError: # not a float pass Sturla -- https://mail.python.org/mailman/listinfo/python-list
