Question

I need help explaining this question and code: The try-except statements are helpful in handling errors that are detected during execution. What are the two categories of errors when debugging code? How can the try-except statements handle errors in Python? Provide a code example that supports your comments...Thanks in advance

Answer 1

The two categories of errors when debugging code:

1. Compile time errors
2. Runtime time errors

1.Compile time errors

Answer: When we write any code, our source code file is given to a program called ‘compiler’. Compiler checks whether everything written in a file is correct or according to the rules specified by that programming language. Rules are-> how we are suppose to write code. For example: declaring variables, initializing them, writing functions. Let’s see the following example to understand this better:

1. In C++ programming language function is written in following way:

Type function_name([type variable])

{

//Function body;

}

Eg.:       int addition(int a, int b)

{

               return (a+b);

}

2. In Python function is written in following way:

def function_name([variable]):

               #function body

E.g.:     def addition(x,b):

                              print(x+b)

So, as we can see for different programming languages there is a different way to write a function. And if do some mistake while writing them, then at the time of compilation an error would get generated saying ‘incorrect syntax’. This is because the compiler checks whether everything is syntactically correct. So, what can go wrong at compile time: 1) Syntax errors, 2) type checking errors.

E.g.:       string a=”hello”

int b=a

     In above case, we are trying to assign a string type value to an integer type variable. So there is a type checking error.

2. Runtime errors

Answer: If the program is correct for the compiler and there is no compile time error, then program is now passed for the execution to the interpreter in Python. The program may exit unexpectedly during execution if it encounters a runtime error – a problem which was not detected when the program was parsed, but is only revealed when a particular line is executed.

Runtime errors are generated due to:

1. Divide by zero operation
2. Accessing array element which does not exists
3. Trying to open a file which is not present

For example:

               A=10

               B=0

               C=A/B

               print (c)

In above example, no compile time error is generated because for compiler, everything is syntactically correct. But while execution interpreter finds it semantically incorrect as we are trying to divide ‘A’ by 0. So, the exception of divide by zero would get generated.

try-except statements:

To deal with exceptions try-except can help us.

               try : this block contains the code which may generate an exception.

               except : this block contains the code to handle the exception.

E.g.: If we write a program where we are using a variable without declaring it before. We will try this a) without try-except and b) with try-except

a) without try-except

In [1]: print(x) Name Error Traceback (most recent call last) <ipython-input-1-fc17d851ef81> in <module> ----> 1 print(x) NameError: name 'x' is not defined

As we can see, print(x) is trying to print the value of variable which is not declared or initialized before. So program is generation error and has stopped it’s execution.

b) with try-except

In [2]: try: print(x) except: print("An exception occurred") An exception occurred

When we write the statement which may generate an exception in a try block. Then when such statement is executed the program control is passed to the ‘except’ block. And statements from except block get executed. Hence, it avoids the abnormal interruption in the program.

See following example:

1. Division by zero without try-except:

def divide_operation(a,b): C=a/b; print("Result of", a,"/",b," is: ",c) print("End of the program") divide_operation (10,0) - - - - - - - - - - - - - - - ZeroDivisionError Traceback (most recent call last) <ipython-input-11-4d073dc219d1> in <module> 4 print("End of the program") 5 ----> 6 divide_operation(10,) <ipython-input-11-4d073dc219d1> in divide_operation(a, b) 1 def divide_operation(a,b): ----> 2 c=a/b; print("Result of",a,"/",b," is: ",c) print("End of the program") Hamin ZeroDivisionError: division by zero

As we can see, as program has stopped abnormally , it is not printing the line ‘End of the program’.

2. Division by zero with try-except:

def divide_operation(a,b): try: C=a/b; print("Result of",a,"/",b," is: ",) except: print("Please don't pass second parameter as zero") print("End of the program") divide_operation (10,0) Please don't pass second parameter as zero End of the program

Even if exception occurred, ‘End of the program’ gets printed in the screen.

Below is code in the screenshot :

def divide_operation(a,b):
try:
c=a/b;
print("Result of",a,"/",b," is: ",c)
  
except:
print("Please don't pass second parameter as zero")
print("End of the program")

divide_operation(10,0)

def divide_operation(a,b): try: C=a/b; print("Result of",a,"/",b," is: ",) except: print("Please don't pass second parameter as zero") print("End of the program") divide_operation (10,0) Please don't pass second parameter as zero End of the program