Python Dictionaries

A dictionary is a set of unordered key, value pairs. In a dictionary, the keys must be unique and they are stored in an unordered manner.

In this tutorial you will learn the basics of how to use the Python dictionary.

Creating a Dictionary:

dict1

Accessing Items:
You can access the items of a dictionary by referring to its key name, inside square brackets:

dict2

Updating Dictionary:
You can update a dictionary by adding a new entry or a key-value pair, modifying an existing entry, or deleting an existing entry as shown below in the simple example −

dict3

Loop Through a Dictionary:
You can loop through a dictionary by using a for loop.When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

dict4.JPG

Check if Exists:

You can test the presence of a key using ‘in’ or ‘not in’

dict5

Restrictions on Dictionary Keys:
Almost any type of value can be used as a dictionary key in Python. As an example,  integer, float, and Boolean objects are used as keys:

dict6

However, there are a couple restrictions that dictionary keys must abide by.

First, a given key can appear in a dictionary only once. Duplicate keys are not allowed. A dictionary maps each key to a corresponding value, so it doesn’t make sense to map a particular key more than once.
You could see below that when you assign a value to an already existing dictionary key, it does not add the key a second time, but replaces the existing value:

dict7

Restrictions on Dictionary Values:
By contrast, there are no restrictions on dictionary values. Literally none at all. A dictionary value can be any type of object Python supports, including mutable types like lists and dictionaries, and user-defined objects.There is also no restriction against a particular value appearing in a dictionary multiple times.

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Tuple in Python

Tuples in Python are immutable sequences of random objects. Once created, the objects within them cannot be replaced or removed,and new elements cannot be added.

Tuples have a similar syntax to lists except that they are delimited by parentheses rather than square brackets.Here’s a literal tuple containing a string, a float, and an integer.
We can access the elements of a tuple by zero-based index using square brackets, and we can determine the number of elements in the tuple using the built-in len function. We can iterate over tuples using the for loop, and we can concatenate tuples using the plus operator.

ex1

Sometimes a single element tuple is required. To write this, we can’t just use a simple number in parentheses. This is because Python pauses that as an integer enclosed in the president’s controlling parentheses of a math expression. To create a single element tuple, we make use of the trailing comma separator, which we’re allowed to use when specifying literal tuples, lists, and dictionaries.

A single element with a trailing comma is passed as a single element tuple. This leaves us with the problem of how to specify an empty tuple. In actuality the answer is simple.
We just use empty parentheses. here is the demo:

ex2

In many cases, the parentheses of literal tuples may be omitted. This feature is often used when returning multiple values from a function.

Here we make a function to return the minimum and maximum values of a series, the hard work being done by the two built-in functions min and max. Returning multiple values as tuple is often used in conjunction with a wonderful feature of Python called tuple unpacking.Tuple unpacking is a destructuring operation, which allows us to unpack data structures into named references. For example, we can assign the result of our minmax function to two new references like this.

ex3

Tuple unpacking works with arbitrarily nested tuples, although not with other data structures. Should you need to create a tuple from an existing collection object such as a list, you can use the tuple constructor, here also shown for strings.

ex4

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First Program with Python:

Lets begin our first program with some of String operations.Python has a built in String class named “str” with many handy features.String literals can be enclosed by either double or single quotes, although single quotes are more commonly used. if you want to use Multi line String then you have to use triple quotes.

First Program

Lets assign three different strings to three different variables and print them.
To start with, open Python IDLE under Start –>Programs
or Type Python Under Run prompt

IDLE is an Interactive interpreter, however, you can’t execute more than one statement at a time.
If you want to execute a multi line code program, just copy and paste the below code by opening a new file (CTRL+N) and save it. Then, you can execute the code in the file with ‘key board short cut F5’. output can be seen in the IDLE as shown below:

str1='Single Quote'
str2="Double Quotes"
str3='''This is sentence has more
than one line '''
print(str1)
print(str2)
print(str3)

 
First program

If you face any error while executing the code or any doubts ,post your query in comments section , happy to assist you.

My First blog post – SQLZealot

Hi Everyone,

Hope all are doing good.

I finally decided to blog my experiences in SQL Server here. During MVP meet Jan 2015, I have been inspired by two of SQL MVP fellows – Visakh & Madhivanan on sharing the experiences through blogs with more details. Thanks to both of you motivating me on the same.

Here, I will be sharing my experience and learning for my future reference and for community purposes as well. Hope you all will be enjoying the site. Please share your thoughts on the same.

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