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To create instances of a class, you call the class using class name and pass in whatever arguments its __init__ method accepts."This would create first object of Employee class"emp1 = Employee("Zara",
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The class statement creates a new class definition. The name of the class immediately follows the keyword class followed by a colon as follows −class ClassName:'Optional class documentation string'c
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Class − A user-defined prototype for an object that defines a set of attributes that characterize any object of the class. The attributes are data members (class variables and instance variables) an
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Python has been an object-oriented language since it existed. Because of this, creating and using classes and objects are downright easy. This chapter helps you become an expert in using Python's obje
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Python also allows you to create your own exceptions by deriving classes from the standard built-in exceptions.Here is an example related to RuntimeError. Here, a class is created that is subclassed f
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You can raise exceptions in several ways by using the raise statement. The general syntax for the raise statement is as follows.Syntaxraise [Exception [, args [, traceback]]]Here, Exception is the typ
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An exception can have an argument, which is a value that gives additional information about the problem. The contents of the argument vary by exception. You capture an exception's argument by supplyin
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If you have some suspicious code that may raise an exception, you can defend your program by placing the suspicious code in a try: block. After the try: block, include an except: statement, followed b
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An exception is an event, which occurs during the execution of a program that disrupts the normal flow of the program's instructions. In general, when a Python script encounters a situation that it ca
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When it encounters an assert statement, Python evaluates the accompanying expression, which is hopefully true. If the expression is false, Python raises an AssertionError exception.The syntax for asse
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An assertion is a sanity-check that you can turn on or turn off when you are done with your testing of the program.The easiest way to think of an assertion is to liken it to a raise-if statement (or t
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Python provides two very important features to handle any unexpected error in your Python programs and to add debugging capabilities in them −Exception Handling − This would be covered in this tut
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There are three important sources, which provide a wide range of utility methods to handle and manipulate files & directories on Windows and Unix operating systems. They are as follows −File Obj
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The rmdir() method deletes the directory, which is passed as an argument in the method.Before removing a directory, all the contents in it should be removed.Syntaxos.rmdir('dirname')
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The getcwd() method displays the current working directory.Syntaxos.getcwd()
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You can use the chdir() method to change the current directory. The chdir() method takes an argument, which is the name of the directory that you want to make the current directory.Syntaxos.chdir("new
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All files are contained within various directories, and Python has no problem handling these too. The os module has several methods that help you create, remove, and change directories.The mkdir() Met
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You can use the remove() method to delete files by supplying the name of the file to be deleted as the argument.Syntaxos.remove(file_name)
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Python os module provides methods that help you perform file-processing operations, such as renaming and deleting files.To use this module you need to import it first and then you can call any related
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The tell() method tells you the current position within the file; in other words, the next read or write will occur at that many bytes from the beginning of the file.The seek(offset[, from]) method ch
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The read() method reads a string from an open file. It is important to note that Python strings can have binary data. apart from text data.SyntaxfileObject.read([count])Here, passed parameter is the n
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The file object provides a set of access methods to make our lives easier. We would see how to use read() and write() methods to read and write files.The write() MethodThe write() method writes any st
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The close() method of a file object flushes any unwritten information and closes the file object, after which no more writing can be done.Python automatically closes a file when the reference object o
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Once a file is opened and you have one file object, you can get various information related to that file.Here is a list of all attributes related to file object −Sr.No.Attribute & Desc
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Before you can read or write a file, you have to open it using Python's built-in open() function. This function creates a file object, which would be utilized to call other support methods associated
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Until now, you have been reading and writing to the standard input and output. Now, we will see how to use actual data files.Python provides basic functions and methods necessary to manipulate files b
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The input([prompt]) function is equivalent to raw_input, except that it assumes the input is a valid Python expression and returns the evaluated result to you.#!/usr/bin/pythonstr = input("Enter your
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The raw_input([prompt]) function reads one line from standard input and returns it as a string (removing the trailing newline).#!/usr/bin/pythonstr = raw_input("Enter your input: ")print "Received inp
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Printing to the ScreenThe simplest way to produce output is using the print statement where you can pass zero or more expressions separated by commas. This function converts the expressions you pass i
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A package is a hierarchical file directory structure that defines a single Python application environment that consists of modules and subpackages and sub-subpackages, and so on.Consider a file Pots.p
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When the module is imported into a script, the code in the top-level portion of a module is executed only once.Therefore, if you want to reexecute the top-level code in a module, you can use the
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The globals() and locals() functions can be used to return the names in the global and local namespaces depending on the location from where they are called.If locals() is called from within a functio
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The dir() built-in function returns a sorted list of strings containing the names defined by a module.The list contains the names of all the modules, variables and functions that are defined in a modu
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Variables are names (identifiers) that map to objects. A namespace is a dictionary of variable names (keys) and their corresponding objects (values).A Python statement can access variables in a local
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The PYTHONPATH is an environment variable, consisting of a list of directories. The syntax of PYTHONPATH is the same as that of the shell variable PATH.Here is a typical PYTHONPATH from a Windows syst
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xWhen you import a module, the Python interpreter searches for the module in the following sequences −The current directory.If the module isn't found, Python then searches each directory in the shel
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You can use any Python source file as a module by executing an import statement in some other Python source file. The import has the following syntax −import module1[, module2[,... moduleN]When the
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A module allows you to logically organize your Python code. Grouping related code into a module makes the code easier to understand and use. A module is a Python object with arbitrarily named attribut
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The statement return [expression] exits a function, optionally passing back an expression to the caller. A return statement with no arguments is the same as return None.All the above examples are not
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These functions are called anonymous because they are not declared in the standard manner by using the def keyword. You can use the lambda keyword to create small anonymous functions.1. Lambda forms c
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You may need to process a function for more arguments than you specified while defining the function. These arguments are called variable-length arguments and are not named in the function definition,
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A default argument is an argument that assumes a default value if a value is not provided in the function call for that argument. The following example gives an idea on default arguments, it prints de
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Variables that are defined inside a function body have a local scope, and those defined outside have a global scope.This means that local variables can be accessed only inside the function in which th
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All variables in a program may not be accessible at all locations in that program. This depends on where you have declared a variable.The scope of a variable determines the portion of the program wher
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The statement return [expression] exits a function, optionally passing back an expression to the caller. A return statement with no arguments is the same as return None.
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These functions are called anonymous because they are not declared in the standard manner by using the def keyword. You can use the lambda keyword to create small anonymous functions.1. Lambda forms c
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You may need to process a function for more arguments than you specified while defining the function. These arguments are called variable-length arguments and are not named in the function definition,
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A default argument is an argument that assumes a default value if a value is not provided in the function call for that argument. The following example gives an idea on default arguments, it prints de
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Keyword arguments are related to the function calls. When you use keyword arguments in a function call, the caller identifies the arguments by the parameter name.This allows you to skip arguments or p
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Required arguments are the arguments passed to a function in correct positional order. Here, the number of arguments in the function call should match exactly with the function definition.To call the