[Tut] How to Create a Dictionary from two Lists

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How to Create a Dictionary from two Lists

In this article, you’ll learn how to create a Dictionary from two (2) Lists in Python.

To make it more fun, we have the following running scenario:

Biogenix, a Lab Supplies company, needs to determine the best element from the Periodic Table for producing a new product. They have two (2) lists. The Element Name, the other Atomic Mass. They would prefer this in a Dictionary format.

For simplicity, this article uses 10 of the 118 elements in the Periodic Table.

Question: How would we create a Dictionary from two (2) Lists?

We can accomplish this task by one of the following options:

• Method 1: Use
  Code:

  dict()
  and
  Code:

  zip()
  
  
  
• Method 2: Use Dictionary Comprehension
  
  
• Method 3: Use Generator Expression with
  Code:

  dict()
  and
  Code:

  zip()
  
  
  
• Method 4: Use Lambda
  

Method 1: Use dict() and zip()

This method uses

Code:

zip()

to merge two (2) lists into an iterable object and (

Code:

dict()

) to convert it into a Dictionary as key:value pairs.

Code:

el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson'] el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216] merge_lists = zip(el_name, el_atom) new_dict = dict(merge_lists) for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

• Lines [1-2] create two (2) lists containing the Element Name (
  Code:

  el_name
  ) and corresponding Atomic Mass (
  Code:

  el_atom
  ), respectively.
  
  
• Line [3] merges the two (2) lists using
  Code:

  zip()
  and converts them into an iterable object. The results save to
  Code:

  merge_lists
  .
  
  
• Line [4] converts
  Code:

  merge_lists
  into a Dictionary (
  Code:

  dict())
  . The results save to
  Code:

  new_dict
  as key:value pairs.
  
  
• Line [5] instantiates a For loop to return the key:value pairs from
  Code:

  new_dict
  .
  • Each iteration outputs the key:value pair in a column format to the terminal.
    

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182

Method 2: Use Dictionary Comprehension

This method uses https://blog.finxter.com/zip-unzip-python/Dictionary Comprehension to merge two (2) lists into an iterable object and convert it into a Dictionary as key:value pairs. A great one-liner!

Code:

el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson'] el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216] new_dict = {el_name[i]: el_atom[i] for i in range(len(el_name))} for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

• Lines [1-2] create two (2) lists containing the Element Name (
  Code:

  el_name
  ) and the corresponding Atomic Mass (
  Code:

  el_atom
  ), respectively.
  
  
• Line [3] merges the lists as key:value pairs and converts them into a Dictionary. The results save to
  Code:

  new_dict
  .
  
  
• Line [4] instantiates a For loop to return the key:value pairs from
  Code:

  new_dict
  .
  • Each iteration outputs the key:value pair in a column format to the terminal.
    

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182

Method 3: Use Generator Expression with zip() and dict()

This method uses a Generator Expression to merge two (2) lists
into an iterable object (

Code:

zip()

) and convert it into a Dictionary (

Code:

dict()

) as key:value pairs.

Code:

el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson'] el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216] gen_exp = dict(((k, v) for k, v in zip(el_name, el_atom))) for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

• Lines [1-2] create two (2) lists containing the Element Name (
  Code:

  el_name
  ) and the corresponding Atomic Mass (
  Code:

  el_atom
  ) respectively.
  
  
• Line [3] uses a Generator Expression to merge the lists (
  Code:

  zip()
  ) and create an iterable object. The object converts into a Dictionary (
  Code:

  dict()
  ) and saves back to
  Code:

  gen_exp
  .
  
  
• Line [5] instantiates a For loop to return the key:value pairs from
  Code:

  new_dict
  .
  • Each iteration outputs the key:value pair in a column format to the terminal.
    

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182



Method 4: Use a Lambda

This method uses a Lambda to merge two (2) lists into an iterable object (

Code:

zip()

) and convert it into a Dictionary (

Code:

dict()

) as key:value pairs.

Code:

el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson'] el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216] new_dict = dict((lambda n, a: {name: el_atom for name, el_atom in zip(n, a)})(el_name, el_atom)) for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

• Lines [1-2] create two (2) lists containing the Element Name (
  Code:

  el_name
  ) and the corresponding Atomic Mass (
  Code:

  el_atom
  ) respectively.
  
  
• Line [3] uses a lambda to merge the lists (
  Code:

  zip()
  ) and create an iterable object. The results save to a Dictionary
  Code:

  new_dict
  as key:value pairs.
  
  
• Line [4] instantiates a For loop to return the key:value pairs from
  Code:

  new_dict
  .
  • Each iteration outputs the key:value pair in a column format to the terminal.
    

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182



Summary

After reviewing the above methods, we decide that Method 2 is best suited: minimal overhead and no additional functions required.

Problem Solved! Happy Coding!