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Mastering Python: Annotations, Errors and Environment

bookHandling

Let's consider Python tools that help us to control code execution and errors.

Error Handling Structure

There are different keywords are used to control program errors:

  • try: this keyword is used for the code block where we expect the error.

  • except: this keyword is used for the code block executed if an error is raised.

  • else: this keyword is used to perform certain logic if errors are not raised.

  • finally: this keyword is used for the code block that always executes after all structure.

try and except

These are the main keywords for error handling, the try code block waits for errors, and the except catches it:


              
12345678

            
print("Code above is executed")

try:
    1 / 0
except:
    print("Error is catched")

print("Code below is executed")
copy

The interpreter is not stopped after the ZeroDivisionError raising because the except keyword caught it.

Note

Don't try to put all your code inside the try block - this will lead to unexpected consequences and can break the program.

If the try block is executed without errors, the except block will not be executed.


              
1234

            
try:
    print("No errors")
except:
    print("Error is catched")
copy

The try block does not roll back executed code. All the code lines before an error are executed:


              
1234567891011

            
lst = []

try:
    lst.append("first")  # executed
    lst.append("second")  # executed
    1 / 0  # error
    lst.append("third")  # not executed
except:
    print("Error caught")

print(lst)
copy

Note

The try block raises the exactly one error because executing stops after an error.

else and finally

The else and finally blocks are optional and used less often.


              
12345678910

            
try:
    print("try: Start")
#    1 / 0
    print("try: End")
except:
    print("except: Error is raised")
else:
    print("else: The try block is executed succesfuly")
finally:
    print("finally: Always executed")
copy

You can add and remove comments in the example above to understand how it works.

1. The try code block is used to...

2. The except code block is used to...

3. The else code block is used to...

4. The finally code block is used to...

question mark

The try code block is used to...

Select the correct answer

question mark

The except code block is used to...

Select the correct answer

question mark

The else code block is used to...

Select the correct answer

question mark

The finally code block is used to...

Select the correct answer

Was alles duidelijk?

Hoe kunnen we het verbeteren?

Bedankt voor je feedback!

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bookHandling

Veeg om het menu te tonen

Let's consider Python tools that help us to control code execution and errors.

Error Handling Structure

There are different keywords are used to control program errors:

  • try: this keyword is used for the code block where we expect the error.

  • except: this keyword is used for the code block executed if an error is raised.

  • else: this keyword is used to perform certain logic if errors are not raised.

  • finally: this keyword is used for the code block that always executes after all structure.

try and except

These are the main keywords for error handling, the try code block waits for errors, and the except catches it:


              
12345678

            
print("Code above is executed")

try:
    1 / 0
except:
    print("Error is catched")

print("Code below is executed")
copy

The interpreter is not stopped after the ZeroDivisionError raising because the except keyword caught it.

Note

Don't try to put all your code inside the try block - this will lead to unexpected consequences and can break the program.

If the try block is executed without errors, the except block will not be executed.


              
1234

            
try:
    print("No errors")
except:
    print("Error is catched")
copy

The try block does not roll back executed code. All the code lines before an error are executed:


              
1234567891011

            
lst = []

try:
    lst.append("first")  # executed
    lst.append("second")  # executed
    1 / 0  # error
    lst.append("third")  # not executed
except:
    print("Error caught")

print(lst)
copy

Note

The try block raises the exactly one error because executing stops after an error.

else and finally

The else and finally blocks are optional and used less often.


              
12345678910

            
try:
    print("try: Start")
#    1 / 0
    print("try: End")
except:
    print("except: Error is raised")
else:
    print("else: The try block is executed succesfuly")
finally:
    print("finally: Always executed")
copy

You can add and remove comments in the example above to understand how it works.

1. The try code block is used to...

2. The except code block is used to...

3. The else code block is used to...

4. The finally code block is used to...

question mark

The try code block is used to...

Select the correct answer

question mark

The except code block is used to...

Select the correct answer

question mark

The else code block is used to...

Select the correct answer

question mark

The finally code block is used to...

Select the correct answer

Was alles duidelijk?

Hoe kunnen we het verbeteren?

Bedankt voor je feedback!

Sectie 3. Hoofdstuk 4
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