questions about Exceptions?
is there a general philosophy as to when to use exceptions and when not to? like here: def Calc(): global nbr try: print eval(nbr) except: print Not computable nbr = i have a calculator and nbr is a string that contains '0123456789+-*/' if the string ends on +-*/ it will throw an exception(unexpected EOF). i could easily prevent the exceptions here with an if-statement, is that preferrable and why? also when u throw exceptions should u catch the speicfic one? i guess only if u want it to do soemthing special since catching only only one exception logicall would abort the program if another one is thrown? -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
In general you should only catch the exceptions you want to catch, therefore avoiding the issue of catching unexpected ones, for instances the programming unexpectandly closing. Well, exception handling is expensive (when it catches one) so it really is up to you. If you are using eval and know it might EOF then you should probably look to handle that. The main IF statement style I can think of (checking the end of the string) wouldn't be much of an improvement. Currently I would be very worried about seeing that code as it breaks a number of conventions. However it depends on the importance of the code to wherever or not you should change this. (Global variable, the use of Eval, the CATCH ALL except and the setting of a global variable at the end.) I've seen a good few (simple and advanced) calculator examples using python on the NET, it might be worth looking at some to see their style of coding a calculator to help your own. -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
def Calc(): global nbr try: print eval(nbr) #a = Label(mygui, text=eval(nbr)) #a.place(relx=0.4, rely=0.1, anchor=CENTER) except: print Not computable nbr = def Erase(): global nbr nbr = Seems to me you could be better off passing a parameter and a return statement of None (or your parameter cleaned) for those functions, which should work. Given an input, Eval it and then return None. That way you wouldn't need the Erase... -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
On 10 Apr, 12:38, [EMAIL PROTECTED] wrote: def Calc(): global nbr try: print eval(nbr) #a = Label(mygui, text=eval(nbr)) #a.place(relx=0.4, rely=0.1, anchor=CENTER) except: print Not computable nbr = def Erase(): global nbr nbr = Seems to me you could be better off passing a parameter and a return statement of None (or your parameter cleaned) for those functions, which should work. Given an input, Eval it and then return None. That way you wouldn't need the Erase... the erase() id alwys need if u wanna abort whilst u wrote something. -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
On 10 Apr, 10:51, [EMAIL PROTECTED] wrote: In general you should only catch the exceptions you want to catch, therefore avoiding the issue of catching unexpected ones, for instances the programming unexpectandly closing. Well, exception handling is expensive (when it catches one) so it really is up to you. If you are using eval and know it might EOF then you should probably look to handle that. The main IF statement style I can think of (checking the end of the string) wouldn't be much of an improvement. Currently I would be very worried about seeing that code as it breaks a number of conventions. However it depends on the importance of the code to wherever or not you should change this. (Global variable, the use of Eval, the CATCH ALL except and the setting of a global variable at the end.) I've seen a good few (simple and advanced) calculator examples using python on the NET, it might be worth looking at some to see their style of coding a calculator to help your own. i know about the GLOBAL stuff, i might rewrite the program using classes later so i can avoid this. i am mainly playin with tkinter for now. i was thinking the same check with if at the beginning and end of the string so there isnt a */ but also if someone uses /// or soemthing like that in the middle it crashes so it is hard to cover every case, esp since **5 means ^5. is the use of if also expensive? -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
here is the whole code: from __future__ import division import Tkinter from Tkinter import * mygui = Tkinter.Tk() mygui.title(Calculator) w = Label(mygui, text=Answer: ) w.place(relx=0.15, rely=0.1, anchor=CENTER) nbr = def Disp(nstr): global nbr nbr=nbr+nstr print You need to seek help!,nbr def Calc(): global nbr try: print eval(nbr) #a = Label(mygui, text=eval(nbr)) #a.place(relx=0.4, rely=0.1, anchor=CENTER) except: print Not computable nbr = def Erase(): global nbr nbr = b = Button(mygui, text=1,command=lambda n='1':Disp(n), width=2, height=1) b.place(relx=0.1, rely=0.2, anchor=CENTER) b = Button(mygui, text=2,command=lambda n='2':Disp(n), width=2, height=1) b.place(relx=0.2, rely=0.2, anchor=CENTER) b = Button(mygui, text=3,command=lambda n='3':Disp(n), width=2, height=1) b.place(relx=0.3, rely=0.2, anchor=CENTER) b = Button(mygui, text=+,command=lambda n='+':Disp(n), width=2, height=1) b.place(relx=0.4, rely=0.2, anchor=CENTER) b = Button(mygui, text=4,command=lambda n='4':Disp(n), width=2, height=1) b.place(relx=0.1, rely=0.3, anchor=CENTER) b = Button(mygui, text=5,command=lambda n='5':Disp(n), width=2, height=1) b.place(relx=0.2, rely=0.3, anchor=CENTER) b = Button(mygui, text=6,command=lambda n='6':Disp(n), width=2, height=1) b.place(relx=0.3, rely=0.3, anchor=CENTER) b = Button(mygui, text=-,command=lambda n='-':Disp(n), width=2, height=1) b.place(relx=0.4, rely=0.3, anchor=CENTER) b = Button(mygui, text=7,command=lambda n='7':Disp(n), width=2, height=1) b.place(relx=0.1, rely=0.4, anchor=CENTER) b = Button(mygui, text=8,command=lambda n='8':Disp(n), width=2, height=1) b.place(relx=0.2, rely=0.4, anchor=CENTER) b = Button(mygui, text=9,command=lambda n='9':Disp(n), width=2, height=1) b.place(relx=0.3, rely=0.4, anchor=CENTER) b = Button(mygui, text=*,command=lambda n='*':Disp(n), width=2, height=1) b.place(relx=0.4, rely=0.4, anchor=CENTER) b = Button(mygui, text=0,command=lambda n='0':Disp(n), width=2, height=1) b.place(relx=0.1, rely=0.5, anchor=CENTER) b = Button(mygui, text=C,command=Erase, width=2, height=1) b.place(relx=0.2, rely=0.5, anchor=CENTER) b = Button(mygui, text=^.5,command=lambda n='**.5':Disp(n), width=2, height=1) b.place(relx=0.3, rely=0.5, anchor=CENTER) b = Button(mygui, text=/,command=lambda n='/':Disp(n), width=2, height=1) b.place(relx=0.4, rely=0.5, anchor=CENTER) b = Button(mygui, text==,command=Calc, width=2, height=1) b.place(relx=0.2, rely=0.7, anchor=CENTER) mygui.mainloop() -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
the erase() id alwys need if u wanna abort whilst u wrote something. But if it is meant to only evaluate once you've pressed the enter key (I take it?) you shouldn't need that. And if you are to abort while evaluating it will not do that. -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
On 10 Apr, 13:15, [EMAIL PROTECTED] wrote:
the erase() id alwys need if u wanna abort whilst u wrote something.
But if it is meant to only evaluate once you've pressed the enter key
(I take it?) you shouldn't need that. And if you are to abort while
evaluating it will not do that.
CHANGED IT NOW TO A MUCH BETTER SOLUTION(will see if i can make a
better solution with the buttons, hate big blocks of similarlooking
code):
from __future__ import division
import Tkinter
from Tkinter import *
mygui = Tkinter.Tk()
mygui.title(Calculator)
l = Label(mygui, text=Answer: )
l.place(relx=0.15, rely=0.2, anchor=CENTER)
e = Entry(mygui)
e.place(relx=0.4, rely=0.1, anchor=CENTER)
def Disp(nstr):
e.insert(END, nstr)
def Calc():
expr=e.get()
try:
b = Label(mygui, text=eval(expr))
b.place(relx=0.4, rely=0.2, anchor=CENTER)
except:
b = Label(mygui, text=Not computable)
b.place(relx=0.4, rely=0.2, anchor=CENTER)
def Erase():
e.delete(0,END)
b = Button(mygui, text=1,command=lambda n='1':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.4, anchor=CENTER)
b = Button(mygui, text=2,command=lambda n='2':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.4, anchor=CENTER)
b = Button(mygui, text=3,command=lambda n='3':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.4, anchor=CENTER)
b = Button(mygui, text=+,command=lambda n='+':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.4, anchor=CENTER)
b = Button(mygui, text=4,command=lambda n='4':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.5, anchor=CENTER)
b = Button(mygui, text=5,command=lambda n='5':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.5, anchor=CENTER)
b = Button(mygui, text=6,command=lambda n='6':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.5, anchor=CENTER)
b = Button(mygui, text=-,command=lambda n='-':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.5, anchor=CENTER)
b = Button(mygui, text=7,command=lambda n='7':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.6, anchor=CENTER)
b = Button(mygui, text=8,command=lambda n='8':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.6, anchor=CENTER)
b = Button(mygui, text=9,command=lambda n='9':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.6, anchor=CENTER)
b = Button(mygui, text=*,command=lambda n='*':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.6, anchor=CENTER)
b = Button(mygui, text=0,command=lambda n='0':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.7, anchor=CENTER)
b = Button(mygui, text=C,command=Erase, width=2, height=1)
b.place(relx=0.2, rely=0.7, anchor=CENTER)
b = Button(mygui, text=^,command=lambda n='**':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.7, anchor=CENTER)
b = Button(mygui, text=/,command=lambda n='/':Disp(n), width=2,
height=1)
b.place(relx=0.4, rely=0.7, anchor=CENTER)
b = Button(mygui, text=.,command=lambda n='.':Disp(n), width=2,
height=1)
b.place(relx=0.1, rely=0.8, anchor=CENTER)
b = Button(mygui, text=(,command=lambda n='(':Disp(n), width=2,
height=1)
b.place(relx=0.2, rely=0.8, anchor=CENTER)
b = Button(mygui, text=),command=lambda n=')':Disp(n), width=2,
height=1)
b.place(relx=0.3, rely=0.8, anchor=CENTER)
b = Button(mygui, text==,command=Calc, width=2, height=1)
b.place(relx=0.4, rely=0.8, anchor=CENTER)
mygui.mainloop()
--
http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
from __future__ import division import Tkinter from Tkinter import * mygui = Tkinter.Tk() mygui.title(Calculator) l = Label(mygui, text=Answer: ) l.place(relx=0.15, rely=0.2, anchor=CENTER) e = Entry(mygui) e.place(relx=0.4, rely=0.1, anchor=CENTER) def Disp(nstr): e.insert(END, nstr) def Calc(): expr=e.get() try: b = Label(mygui, text=eval(expr)) b.place(relx=0.4, rely=0.2, anchor=CENTER) except: b = Label(mygui, text=Not computable) b.place(relx=0.4, rely=0.2, anchor=CENTER) def Erase(): e.delete(0,END) x = 0.1 y = 0.4 for char in '123+456-789*0^./()': b = Button(mygui, text=char,command=lambda n=char:Disp(n), width=2, height=1) b.place(relx=x, rely=y, anchor=CENTER) x=x+0.1 if x==0.5: x=0.1 y=y+0.1 b = Button(mygui, text=C,command=Erase, width=2, height=1) b.place(relx=0.3, rely=0.8, anchor=CENTER) b = Button(mygui, text==,command=Calc, width=2, height=1) b.place(relx=0.4, rely=0.8, anchor=CENTER) mygui.mainloop() -- http://mail.python.org/mailman/listinfo/python-list
Re: questions about Exceptions?
On 10 Apr, 12:38, [EMAIL PROTECTED] wrote: def Calc(): global nbr try: print eval(nbr) #a = Label(mygui, text=eval(nbr)) #a.place(relx=0.4, rely=0.1, anchor=CENTER) except: print Not computable nbr = def Erase(): global nbr nbr = Seems to me you could be better off passing a parameter and a return statement of None (or your parameter cleaned) for those functions, which should work. Given an input, Eval it and then return None. That way you wouldn't need the Erase... i never really got what u meant by this? -- http://mail.python.org/mailman/listinfo/python-list
