The Python dictionary is a built-in data type. It defines a one-to-one relationship between keys and values. Dictionaries contain a pair of keys and their corresponding values. It stores elements in key and value pairs. The keys are unique whereas values can be duplicate. The key accesses the dictionary elements.

Keys index dictionaries.

Let's take an example.

The following example contains some keys Country Hero & Cartoon. Their corresponding values are India, Modi, and Rahul respectively.

Pass specifies a Python statement without operations. It is a placeholder in a compound statement. If we want to create an empty class or functions, this pass keyword helps to pass the control without error.

The Python docstring is a string literal that occurs as the first statement in a module, function, class, or method definition. It provides a convenient way to associate the documentation.

String literals occurring immediately after a simple assignment at the top are called "attribute docstrings".

String literals occurring immediately after another docstring are called "additional docstrings".

Python uses triple quotes to create docstrings even though the string fits on one line.

Docstring phrase ends with a period (.) and can be multiple lines. It may consist of spaces and other special chars.

Example

Python sequences are accessible using an index in positive and negative numbers. For example, 0 is the first positive index, 1 is the second positive index and so on. For negative indexes -1 is the last negative index, -2 is the second last negative index and so on.

Index traverses from left to right and increases by one until end of the list.

Negative index traverse from right to left and iterate one by one till the start of the list. A negative index is used to traverse the elements into reverse order.

The Python pickle is defined as a module which accepts any Python object and converts it into a string representation. It dumps the Python object into a file using the dump function; this process is called pickling.

The process of retrieving the original Python objects from the stored string representation is called as Unpickling.

Java and Python both are object-oriented programming languages. Let's compare both on some criteria given below:

Help() and dir() both functions are accessible from the Python interpreter and used for viewing a consolidated dump of built-in functions.

Help() function: The help() function is used to display the documentation string and also facilitates us to see the help related to modules, keywords, and attributes.

Dir() function: The dir() function is used to display the defined symbols.

You have to import CGI module to access form fields using FieldStorage class.

Attributes of class FieldStorage for the form:

form.name: The name of the field, if specified.

form.filename: If an FTP transaction, the client-side filename.

form.value: The value of the field as a string.

form.file: file object from which data read.

form.type: The content type, if applicable.

form.type_options: The options of the 'content-type' line of the HTTP request, returned as a dictionary.

form.disposition: The field 'content-disposition'; None, if unspecified.

form.disposition_options: The options for 'content-disposition'.

form.headers: All of the HTTP headers returned as a dictionary.

Python 2.x is an older version of Python. Python 3.x is newer and latest version. Python 2.x is legacy now. Python 3.x is the present and future of this language.

The most visible difference between Python2 and Python3 is in print statement (function). In Python 2, it looks like print "Hello", and in Python 3, it is print ("Hello").

String in Python2 is ASCII implicitly, and in Python3 it is Unicode.

The xrange() method has removed from Python 3 version. A new keyword as is introduced in Error handling.

You have to define an alias for the base class, assign the real base class to it before your class definition, and use the alias throughout your class. You can also use this method if you want to decide dynamically (e.g., depending on availability of resources) which base class to use.

Example