#python

8. Dictionary Data Structure

Dictionaries are used to store data values in key-value pairs

• Duplicate keys are not allowed but values can be duplicated.
• Hetrogeneous objects are allowed for both key and values.
• Insertion order is not preserved
• Dictionaries are mutable
• Indexing and slicing concepts are not applicable

As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

9. Functions

If a group of statements is repeatedly required then it is not recommended to write these statements everytime separately.

We have to define these statements as a single unit, and we can call that unit any number of times based on our requirement without rewriting. This unit is nothing but function.

• The main advantage of functions is code Reusability.
• Python supports 2 types of functions
  1. Built-in Functions
  2. User Defined Functions

Python DateTime module

The datetime classes are categorize into 6 main classes –

• date
  • Its attributes are year, month and day
• time
  • Its attributes are hour, minute, second, microsecond and tzinfo

1. Python OS Module

• Python OS module provides the facility to establish the interaction between the user and the operating system
• It provides functions for creating and removing a directory (folder), fetching its contents, changing and identifying the current directory, etc.

import os

# shows all attribute and method in this module.
print(dir(os))

Handling timezone in Python

UTC, or Coordinated Universal Time, is the primary time standard by which the world regulates date and time.

• astimezone() –> it helps to convert the time of a particular time zone into another time zone
• localtime() –> it helps to get the current local time

2. File Handling

As the part of programming requirement, we have to store our data permanently for future purpose. For this requirement we should go for files.

Files are very common permanent storage areas to store our data.

There are 2 types of file

• Text Files
  • Usually we can use text files to store character data
• Binary Files
  • Usually we can use binary files to store binary data like images,video files, audio files etc..

3. Exception Handling

In any programming language there are 2 types of errors are possible.

1. Syntax Errors
2. Runtime Errors

4. Regular expression

• A Regular Expression (RegEx) is a sequence of characters that defines a search pattern
• RegEx can be used to check if a string contains the specified search pattern.
• Python has a built-in package called re, which can be used to work with Regular Expressions.

If we want to represent a group of Strings according to a particular format/pattern then we should go for Regular Expressions.

Python collection module

• There are 4 basic collection data types
  • List, Tuples, Sets, Dictionary
• Specialised collection data types
  • Counter, OrderedDict, UserDict, UserList, UserString
  • defaultdict, deque, namedtuple(), Chainmap

Deepcopy and Shallow copy

• In case of shallow copy, a reference of object is copied in other object.
  • It means that any changes made to the copied object do reflect in the original object
  • External object id changes but Internal object id remains same
• In case of deep copy, a copy of object is copied in other object.
  • It means that any changes made to the copied object do not reflect in the original object
  • External and internal object ids changes