Essentially I'm just wondering if there's any way to make this code more concise. I don't even really know how to properly ask the question, but is there a module or expression I could write or import to help?
while True:
try:
guess = int(input("Enter a number here: "))
break
except:
print("Please try again.")
In free language it would probably look like:
test:
dothing("user thing")
if issues:
print("try again")
try again
I'm trying to prevent an error from the user typing something like a string and breaking the entire program. If this seems stupid, I apologize; I'm starting to get into Python again after what is essentially years of not using it and I'm probably forgetting something simple.
Thank you guys so much in advance.
Your natural language remembers me old unstructured languages like Fortran 4 or old basics...
In those languages, we used to go to line references:
100 CALL INPUTVAL(IVAL, IERR)
IF IERR == 0 GOTO 200
PRINT 50
50 FORMAT('ERROR TRY AGAIN')
GOTO 100
200 CONTINUE
It may look more natural at first sight, but it soon leads to spaghetti code. That's the reason why clean loops and strutured error handling (try except) were invented. Don't regret the old goto style and stick to standard structured constructs
Related
I am a beginner in coding and I've been learning python just lately.
I tried to do some recursion exercises, my codes run most of the time but there is one thing that is worrying me.
My code is always longer than the one in the solution.
Take this exercise for example
(Write a Python program to get the sum of a non-negative integer.Test Data:sumDigits(345) -> 12sumDigits(45) -> 9)
My answer is this
def sum_num(n,sum1=0):
k=int(n)
if k%10==k:
return sum1+k
else:
sum1+=k%10
k=k//10
return(sum_num(k,sum1))
print(sum_num(2384))
and the solution is this
def sumDigits(n):
if n == 0:
return 0
else:
return n % 10 + sumDigits(int(n / 10))
print(sumDigits(345))
print(sumDigits(45))
print(sumDigits(345))
print(sumDigits(45))
My code run perfectly but it's just longer. My question is 'is it okay to have a long code, if not how can I learn to shorten it'.
Thank you
Well, writing shorter and cleaner code is good practice because when you have long code thats hard to read its going to be harder for you and especially oher people to work with it, and troubleshooting can be really difficult. Think simple and try to write it as clean as it could possibly be. There isnt really a way to LEARN it but practice and studying and just trying to think simple should help.
def travel():
travel.s=0
travel.frate=[]
travel.tr=[]
def accomodation():
print"""specialises
1.place 1
a.hotel 1
b.hotel 2
Hotel1:ac/non ac rooms
Ac.for ac...
Noac.for non ac...."""
hd=[5000,6000]
hg=[4000,7000]
TAc=[1000]
Nac=[400]
ch5=input("Enter your choice")
fav=raw_input("ENter hotel choice")
mode=raw_input("Enter ac/no ac")
if(ch5==1):
for i in hd:
frate=hd[i]+TAc
else:
frate=hd[i]+Nac
if(ch5==2):
for i in range(0,2,1):
frate=hg[i]+TAc
else:
frate=hg[i]+Nac
accomodation()
travel()
When i run the program , i get the error as List Index out of range.but in hd and hg list,there are only two elements, so index number will be from 0 right?? Is there anything i should import?? I even gave statements like this:
travel.frate=travel.hg[i]+TAc
but it still doesn't come.Thank you for your effort.
the indentation is proper now,but the output is still not coming.
The specific issue you are encountering is caused by these lines here:
if(ch5==1):
for i in hd:
frate=hd[i]+TAc
hd[i] looks at hd[5000] and hd[6000] which will throw an IndexError.
But if you fix that, you're going to run into another error, because
frate=hd[i]+TAc
tries to add a list TAc to an integer hd[i], which is an unsupported operation. You probably need frate=hd[i]+TAc[0], or even better, make TAc a number rather than a list. This issue occurs elsewhere in your code as well.
Finally, while not causing explicit issues in your code right now, there are two other problems:
ch5=input("Enter your choice") is dangerous since input tells Python to run whatever code snippet the user enters. In this case, much safer to do ch5=int(raw_input("Enter your choice"))
for i in range(0,2,1): is really for i in range(2): - only use the starting index and jump parameters if you need to change them from their default, namely 0 and 1.
There are other issues like variable scope (you're expecting travel.frate to be modified from within accommodation, but that's not happening) and defining variables in functions like travel.frate (not invalid syntax, but definitely strange) but those are probably better addressed outside of this question.
Running this code a few times presents no issues. Upon attempting to show a friend, it doesn't work. It just hangs after the input. It's worked quite a few times before but never again unfortunately.
I've tried rewriting the code in brackets, rewriting the code to a local directory instead of the Google Drive folder I have and I've even tried rewriting from scratch in regular notepad. All this was tried in case some sort of encoding issue had occured. No such luck. I figure something is wrong with the interpreter but I'm not sure how to remedy the situation.
def bin2dec():
bin = []
a = int(input("What number are you converting to binary?: "))
while a > 0:
if a % 2 == 0:
bin.insert(0, 0)
a = a/2
elif a % 2 == 1:
bin.insert(0, 1)
a = a/2-0.5
else:
#repetition
print("Your binary equivalent is:", bin)
repeat = input("Would you like to convert another binary number?: ")
if repeat == "yes":
bin2dec()
bin2dec()
Oh....welp. It seems the problem was actually that I somehow installed two versions of pythons and I guess they had been interfering with each other. Reason I'm not deleting this Q is because I'm sure I'm not the only one who's made this mistake. However, others have probably made this mistake in an effort to ensure compatibility between versions. Bad idea.
I just came accross the following code in an existent project, which I'm working on:
if True:
x = 5
y = 6
return x+y
else:
return 'Something
Inside the if True are lots of conditions and some will also return the function already.
Why would somebody write in that way? The code contained some other bugs also, but was just wondering about the if True: statement as it didn't make any sense to me. Probably also pretty stupid to ask it, but was wondering hehe.
It might be a remnant of debugging or refactoring. It may be that instead of True, there was orginally a condition or variable there but it has now been replaced by True. The developer perhaps left it there without refactoring or cleaning it up all the way.
If you're free to edit the code as you wish and you're sure that the else is no longer needed, then you can remove it. It indeed makes no sense to have code in your codebase that will never run.
True doesn't necessarily mean True
True = False
if not True :
print "True is false" # This prints ok
Honestly, I don't think anyone would code like this.
Does not make any sense to me, my guess is that someone wanted to have two distinct code paths that he could alternate between a'la using #if 1 .. #else -> #if 0 ... for debugging or such purposes.
Other possibility was that, as #SimeonVisser suggested, the original developer was refactoring or cleaning up the code (and did not have an emulator that allows one to easily remove 1 step of indentation from a block of code)
It could be a flag used for debugging.
It's simply used to ensure that the else: block is never executed.
I have used if True: for some blocks to ensure that my code really does what I want. Usage for debugging or refactoring.
All in all it makes no real sense to use this in an application but for testing or debugging it's somehow acceptable.
Hey I am having problems with calculating the roots of the quadratic equation with the quadratic formula, using python's complex number functionality.
When I try
>>> if root<0:
root=abs(complex(root))
j=complex(0,1)
x1=(-b+sqrt(root))/2*a
x2=(-b-j+sqrt(root))/2*a
else:
I get the error message
SyntaxError: invalid syntax
Then, when I try instead
>>> if root<0:
root=abs(complex(root))
j=complex(0,1)
x1=(-b+j+sqrt(root))/2*a
x2=(-b-j+sqrt(root))/2*a
break
I get the error
SyntaxError: 'break' outside loop
I am trying to put:
else:
x1=(-b+j+sqrt(root))/2*a
x2=(-b-j+sqrt(root))/2*a
under it but it won't work.
Any help please?
Not sure I understand your problem, but it looks like you are not properly indenting -- Python uses white space to mark blocks, so the above should look like:
if root<0:
root=abs(complex(root))
j=complex(0,1)
x1=(-b+j+sqrt(root))/2*a
x2=(-b-j+sqrt(root))/2*a
else:
x1=(-b+j+sqrt(root))/2*a
x2=(-b-j+sqrt(root))/2*a
although that doesn't make sense because x1 and x2 are calculated the same in both branches, and j is not defined in the else branch... so maybe what you really want is
if root<0:
root=abs(complex(root))
j=complex(0,1)
x1=(-b+j+sqrt(root))/2*a
x2=(-b-j+sqrt(root))/2*a
Part of my confusion is the prompt: enter code here -- this is not a standard Python prompt so either you changed your prompt or you are using some other program with your Python. At any rate, hope this helps.
try importing the complex math module, available online in a number of forms. I believe there is an implementation for complex numbers in the standard python distributions, as well as in numpy/scipy. You can also try working out the real and complex components of your roots separately (by including a test based on the value of the discriminant). Also, your if and elif tests are identical.
As #bythenumbers points out, your if and elif conditions are the same. Also, are you getting exceptions or the wrong values? Also also, where you have j+sqrt(root), do you perhaps mean j*sqrt(root)?