003_Python_File_Exception.ipynb

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    "<small><small><i>\n",
    "All the IPython Notebooks in this lecture series by Dr. Milan Parmar are available @ **[GitHub](https://github.com/milaan9/05_Python_Files)**\n",
    "</i></small></small>"
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    "# Python Errors and Built-in Exceptions\n",
    "\n",
    "In this class, you will learn about different types of errors and exceptions that are built-in to Python. They are raised whenever the Python interpreter encounters errors.\n",
    "\n",
    "We can make certain mistakes while writing a program that lead to errors when we try to run it. A python program terminates as soon as it encounters an unhandled error. These errors can be broadly classified into two classes:\n",
    "\n",
    "1. Syntax errors\n",
    "2. Logical errors (Exceptions)"
   ]
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    "## 1. Python Syntax Errors\n",
    "\n",
    "Error caused by not following the proper structure (syntax) of the language is called **syntax error** or **parsing error**.\n",
    "\n",
    "For example:"
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     "ename": "SyntaxError",
     "evalue": "invalid syntax (<ipython-input-1-3e28e520013d>, line 1)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-1-3e28e520013d>\"\u001b[1;36m, line \u001b[1;32m1\u001b[0m\n\u001b[1;33m    if a < 3\u001b[0m\n\u001b[1;37m            ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
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    "if a < 3"
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    "As shown in the example, an arrow indicates where the parser ran into the syntax error.\n",
    "\n",
    "We can notice here that a colon **`:`** is missing in the **`if`** statement."
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    "## 2. Python Logical Errors (Exceptions)\n",
    "\n",
    "Errors that occur at runtime (after passing the syntax test) are called **exceptions** or **logical errors**.\n",
    "\n",
    "For instance, they occur when we try to open a file(for reading) that does not exist (**`FileNotFoundError`**), try to divide a number by zero (**`ZeroDivisionError`**), or try to import a module that does not exist (**`ImportError`**).\n",
    "\n",
    "Whenever these types of runtime errors occur, Python creates an exception object. If not handled properly, it prints a traceback to that error along with some details about why that error occurred.\n",
    "\n",
    "Let's look at how Python treats these errors:"
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    {
     "ename": "ZeroDivisionError",
     "evalue": "division by zero",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mZeroDivisionError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-2-bc757c3fda29>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[1;36m1\u001b[0m \u001b[1;33m/\u001b[0m \u001b[1;36m0\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mZeroDivisionError\u001b[0m: division by zero"
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    "1 / 0"
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     "ename": "FileNotFoundError",
     "evalue": "[Errno 2] No such file or directory: 'imaginary.txt'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-3-2bedf9c67314>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"imaginary.txt\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m: [Errno 2] No such file or directory: 'imaginary.txt'"
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    "open(\"imaginary.txt\")"
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    "## Python Built-in Exceptions\n",
    "\n",
    "Illegal operations can raise exceptions. There are plenty of built-in exceptions in Python that are raised when corresponding errors occur. We can view all the built-in exceptions using the built-in **`local()`** function as follows:\n",
    "\n",
    "```python\n",
    "print(dir(locals()['__builtins__']))\n",
    "```\n",
    "\n",
    "**`locals()['__builtins__']`** will return a module of built-in exceptions, functions, and attributes. **`dir`** allows us to list these attributes as strings.\n",
    "\n",
    "Some of the common built-in exceptions in Python programming along with the error that cause them are listed below:\n",
    "\n",
    "| Exception | Cause of Error |\n",
    "|:----| :--- |\n",
    "| **`AssertionError`** |   Raised when an **`assert`** statement fails.   | \n",
    "| **`AttributeError`** |   Raised when attribute assignment or reference fails.   | \n",
    "| **`EOFError`** |   Raised when the **`input()`** function hits end-of-file condition.   | \n",
    "| **`FloatingPointError`** |   Raised when a floating point operation fails.   | \n",
    "| **`GeneratorExit`** |   Raise when a generator's **`close()`** method is called.   | \n",
    "| **`ImportError`** |   Raised when the imported module is not found.   | \n",
    "| **`IndexError`** |   Raised when the index of a sequence is out of range.   | \n",
    "| **`KeyError`** |   Raised when a key is not found in a dictionary.   | \n",
    "| **`KeyboardInterrupt`** |   Raised when the user hits the interrupt key (**`Ctrl+C`** or **`Delete`**).   | \n",
    "| **`MemoryError`** |   Raised when an operation runs out of memory.   | \n",
    "| **`NameError`** |   Raised when a variable is not found in local or global scope.   | \n",
    "| **`NotImplementedError`** |   Raised by abstract methods.   | \n",
    "| **`OSError`** |   Raised when system operation causes system related error.   | \n",
    "| **`OverflowError`** |   Raised when the result of an arithmetic operation is too large to be represented.   | \n",
    "| **`ReferenceError`** |   Raised when a weak reference proxy is used to access a garbage collected referent.   | \n",
    "| **`RuntimeError`** |   Raised when an error does not fall under any other category.   | \n",
    "| **`StopIteration`** |   Raised by **`next()`** function to indicate that there is no further item to be returned by iterator.   | \n",
    "| **`SyntaxError`** |   Raised by parser when syntax error is encountered.   | \n",
    "| **`IndentationError`** |   Raised when there is incorrect indentation.   | \n",
    "| **`TabError`** |   Raised when indentation consists of inconsistent tabs and spaces.   | \n",
    "| **`SystemError`** |   Raised when interpreter detects internal error.   | \n",
    "| **`SystemExit`** |   Raised by **`sys.exit()`** function.   | \n",
    "| **`TypeError`** |   Raised when a function or operation is applied to an object of incorrect type.   | \n",
    "| **`UnboundLocalError`** |   Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable.   | \n",
    "| **`UnicodeError`** |   Raised when a Unicode-related encoding or decoding error occurs.   | \n",
    "| **`UnicodeEncodeError`** |   Raised when a Unicode-related error occurs during encoding.   | \n",
    "| **`UnicodeDecodeError`** |   Raised when a Unicode-related error occurs during decoding.   | \n",
    "| **`UnicodeTranslateError`** |   Raised when a Unicode-related error occurs during translating.   | \n",
    "| **`ValueError`** |   Raised when a function gets an argument of correct type but improper value.   | \n",
    "| **`ZeroDivisionError`** |   Raised when the second operand of division or modulo operation is zero.   | "
   ]
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   "source": [
    "If required, we can also define our own exceptions in Python. To learn more about them, visit Python **[User-defined Exceptions](https://github.com/milaan9/05_Python_Files/blob/main/005_Python_User_defined_Exceptions.ipynb)**.\n",
    "\n",
    "We can handle these built-in and user-defined exceptions in Python using **`try`**, **`except`** and **`finally`** statements. To learn more about them, visit **[Python try, except and finally statements](https://github.com/milaan9/05_Python_Files/blob/main/004_Python_Exceptions_Handling.ipynb)**."
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