Python Advanced Course - part III.pdf for Python

Python Advanced Course - part III.pdf for Python

• 1.
  Python Advanced Course PartIV Stefano Alberto Russo
• 2.
  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io ● Part I: Object Oriented Programming ○ What is OOP? ○ Logical Example ○ Attributes and methods ○ Why to use objects ○ Defining objects ● Part II: Improving your code ○ Extending objects ○ Lambdas ○ Comprehensions ○ Iterables ○ Properties Outline ● Part III: Exceptions ○ What are exceptions? ○ Handling exceptions ○ Raising exceptions ○ Creating custom exceptions ● Part IV: logging and testing ○ The Python logging module ○ Basics about testing ○ The Python unit-testing module ○ Test-driven development
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exceptions → What are “exceptions”? Exceptions are the “errors” in Python.
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exceptions → What are “exceptions”? Exceptions are the “errors” in Python.
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exceptions → What are “exceptions”? Exceptions are the “errors” in Python. And they are…
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exceptions → What are “exceptions”? Exceptions are the “errors” in Python. And they are… objects
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io As objects, they leverage inheritance. → They all extend the base class “Exception” Examples: Exception ArithmeticError FloatingPointError ZeroDivisionError AttributeError SyntaxError NameError TypeError ValueError Exceptions → What are “exceptions”?
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io The try-except construct allows to handle exceptions. To “catch” them. Exceptions → Handling exceptions
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io The try-except construct allows to handle exceptions. To “catch” them. Exceptions → Handling exceptions Cannot convert my_var to float my_var = 'Hello' try: my_var = float(my_var) except: print('Cannot convert my_var to float')
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io I can react to errors (exceptions): Exceptions → Handling exceptions Cannot convert my_var to float Will use the default value of 0.0 my_var = 'Hello' try: my_var = float(my_var) except: print('Cannot convert my_var to float') print('Will use the default value of 0.0') my_var = 0.0
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io …and I can get the exception inside the “except” branch: Exceptions → Handling exceptions Got error in converting: "could not convert string to float: 'Hello'" Will use the default value of 0.0 my_var = 'Hello' try: my_var = float(my_var) except Exception as e: print('Got error in converting: "{}"'.format(e)) print('Will use the default value of 0.0') my_var = 0.0
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io …and I can get the exception inside the “except” branch: Exceptions → Handling exceptions Got error in converting: "could not convert string to float: 'Hello'" Will use the default value of 0.0 my_var = 'Hello' try: my_var = float(my_var) except Exception as e: print('Got error in converting: "{}"'.format(e)) print('Will use the default value of 0.0') my_var = 0.0 To use the exception inside the “except”, I always have to specify which exception I want to handle, if I want to handle them all then I use the base class Exception.
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io I can indeed handle multiple exceptions in a chain: Exceptions → Handling exceptions try: my_var = float(my_var) except TypeError: print('Wrong type for float conversion: "{}"'.format(type(my_var))) except ValueError: print('Wrong value for float conversion: "{}"'.format(my_var)) except Exception as e: print('Got generic error in converting: "{}"'.format(e))
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io There are two more useful constructs the “else” and the “finally”: Exceptions → Handling exceptions my_file = open('/tmp/tmp.txt', 'w') try: my_file.write(my_string) except Exception as e: print('Got error in writing to file: "{}"'.format(e)) else: print('Success!') finally: my_file.close()
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exceptions can be raised by you as well: Exceptions → Raising exceptions def concat(a,b): if not isinstance(a, str): raise TypeError('First argument not of type string') if not isinstance(b, str): raise TypeError('Second argument not of type string') return a+b print(concat('Hello', 67)) ... TypeError: First argument not of type string
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io You can define custom exceptions by extending the base Exception class Exceptions → Custom exceptions class PortfolioError(Exception): pass class EmptyPortfolioError(PortfolioError): pass
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exceptions → Raising exceptions def do_stuff(portfolio): try: first_portfolio_item = portfolio[0] except IndexError: raise EmptyPortfolioError('Portfolio is empty') from None do_stuff([]) ... __main__.EmptyPortfolioError: Portfolio is empty And you can also catch and re-raise
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io End of part III → Questions? Next: exercise 3
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  Stefano Alberto Russo- @stefanoarusso - sarusso.github.io Exercise 3 Add proper exception handling and raising to the IncrementModel and FitIncrementModel. Try to score up in the autograding!