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Python Dictionaries

Author: Mansoor Ahmed
by Mansoor Ahmed
Posted: Oct 18, 2020
customer 12345
  • A dictionary is a series of pairs of things. It is a collection which is unordered, changeable and indexed.

  • Each pair contains a key—"firstname", "last name" etc.—and a value—"Mansoor", "Ahmed", etc

  • To pick something out of a dictionary, we specify a particular key and

    ask what value is paired with it

  • Dictionaries are written with curly brackets, and they have keys and values.

  • In a dictionary, each chunk is a paired key and value.

  • Notice that the key is followed by a colon:

  • the variable name is singular, not plural

  • All the values are strings, enclosed in quotation marks, and so are all the keys

  • Dictionary’s purpose is to store information that we can later lay our hands on.

  • For example, if someone wants to know the address of "Mansoor Ahmed" how does he will find it?

  • In a dictionary, we pick out an element by specifying its key:

  • address_of_customer = customer_12345 ["address"]

  • print (address_of_customer)

  • The keys can be strings and numbers.

  • To pick out a value, we use the number

  • Values can be numbers, too :

  • To pick out a value, we use the key, a string in this case

  • We can mix strings and numbers any way we want

How to add a key-value pair to a dictionary

  • Let us see we have dictionary

  • customer_12345 = {"first name": "Mansoor", "last name": "Ahmed", "address": "H.No.3 Ibrahim Fibres Ltd Colony"}

  • We can add a new pair by writing

  • customer_12345["city"]= "Faisalabad"

  • We can define an empty dictionary, a dictionary with no key-value pairs:

  • things_to_remember = {}

  • Later, we can fill the dictionary with pairs, adding one at a time

  • things_to_remember[1000] ="highest number"

  • thing_to_remember["last name"]= "Ahmed"

How to delete an element from dictionary:

del customer_12345["address"]

  • It begins with the same keyword:

  • Then comes the name of the dictionary.

  • And the particular piece of information we're after is specified by the key (in the dictionary), in square brackets

  • Then the assignment of the new value.

Looping through a values

  1. customer_12345 = {"first name": "Mansoor", "last name": "Ahmed", "address": "H.No.3 Ibrahim Fibres Ltd Colony"}
  2. for each_value in customer_12345.value():
  3. print (each_valuve)
  • The loop begins with the familiar for:

  • Next comes a variable to store the value for each iteration.

  • Next, the keyword in followed by the name of the dictionary, customer_12345

  • Then a dot…

  • Then the keyword values…

  • then empty parentheses and colon

Looping through keys

  • This is a dictionary

    customer_12345 = {"first name": "Mansoor", "last name": "Ahmed", "address": "H.No.3 Ibrahim Fibres Ltd Colony"}

  • This is the loop:

    for each_key in customer_12345.keys():


  • Python displays:

    first name

    last name


Looping through key-value pairs

  • This is the dictionary we've been working with:

    customer_12345 = {"first name": "Mansoor", "last name": "Ahmed", "address": "H.No.3 Ibrahim Fibres Ltd Colony"}

  • Here's the code for looping through the dictionary and printing all the keys and values:

    for each_key,each_value in customer_12345.items():

    print("The_customer’s" + each_key + " is" + each_value)

  • Following the instructions above, Python displays:

    The customer's first name is Mansoor

    The customer's last name is Ahmed

    The customer's address is H.No.3 Ibrahim Fibres Ltd Colony

Length of Dictionary

  • To determine how many items (key-value pairs) a dictionary has, use the len () function.

    Example: Print the number of items in the dictionary:

  • print(len(thisdict))

How to append a new dictionary to a list of dictionaries

  • To learn how many dictionaries are in the list, we measure the list's length using the keyword len, for length, we write

  • new_customer_id = len(customers)

  • We can create the new dictionary

    new_dictionary = {"customer id": new_customer_id,"first name new_first_name, "last name": new_last_name,"address": new_address,}

  • Finally, we append this new dictionary to the list:

  • customers.append(new_dictionary)

About the Author

Mansoor Ahmed Chemical Engineer,Web developer

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Author: Mansoor Ahmed

Mansoor Ahmed

Member since: Oct 10, 2020
Published articles: 5

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