Sort dictionary Python

da Cristina | Giu 12, 2021 | Python

You can sort a dictionary in Python by key or by value. Let’s do some practical examples of sorting in Python according to our needs.

All the proposed examples can be tested in the online compiler that you will find at the following link: Python compiler online.

First example – Sort a dictionary in Python by key

In this first example we first create a dictionary in Python. We then said to sort by key, so we have to decide whether to follow an ascending or descending order, finally we have to call the function on the dictionary.

So let’s implement a first solution. To sort in ascending order we can use the sorted function on our dictionary, like this:

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

for key in sorted(student):
    print(key, student[key])

What if we want a descending order? Simply use the reverse parameter of the sorted function, setting it to False.

Here is an example of a descending dictionary in Python:

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

for key in sorted(student, reverse = True):
    print(key, student[key])

Second example – Sort a dictionary in Python by key

Let us now seek a second solution to the proposed problem.

First, for example, we could think of using the keys() method on the dictionary, but what happens?

So let’s try it with an example:

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

sorted_key = sorted(student.keys())

for element in sorted_key:
  print(element)

In this case you will have the following output:

age
hobby
mail
name
passion

That is, we will have only the keys ordered in ascending order.

So even if I use the dict () method I won’t be able to sort a dictionary in Python this way.

What if we try to use the values​​() method instead?

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

sorted_values = sorted(student.values())

for element in sorted_values:
  print(element)

The result will be the following:

29
Cristina
coding
codingcreatico@gmail.com
swim

So if I want to sort a dictionary in Python by key what should I do? What other solution can I think of?

We can, for example, use the items() method, which we studied in this lesson: items Python.

We also remind you that this method is used to return the list with all the dictionary keys with their respective values.

After that, we can again convert the pairs of tuples back into a dictionary using the dict () method.

Here is a possible solution to our algorithm:

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

sorted_student = sorted(student.items())
sorted_student_dict = dict(sorted(student.items()))

print(sorted_student_dict)

for element in sorted_student_dict:
  print(element, ': ', sorted_student_dict[element])

So we got all the key tuple pairs, values ​​sorted in ascending order. Then, let’s convert it to a dictionary with the dict () method. So we can sort the dictionary in Python by key.

We use a function to then be able to use it to create the order on multiple dictionaries:

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

def sort_dict(d):
  return dict(sorted(student.items()))

print(sort_dict(student))

Sort a dictionary in Python by key in descending order

This time we use the reverse parameter of sorted to create a descending sort on the dictionaries. In fact, setting it to True the sorting will be descending. By default its value is False.

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

def sort_dict(d):
  return dict(sorted(student.items(), reverse = True))

print(sort_dict(student))

For the sake of completeness we could also pass this parameter to the function, like this:

student = {
    "name": 'Cristina',
    "age": '29',
    "hobby": 'swim',
    "mail": 'codingcreatico@gmail.com',
    "passion": 'coding'
}

def sort_dict(d, rev):
  return dict(sorted(student.items(), reverse = rev))

print(sort_dict(student, True))

Conclusion

In this lesson we have covered some interesting examples of how to sort a dictionary in Python by key, in ascending and descending order.

Some useful links

Python tutorial

Python Compiler

Install Python

Variables

Assignment operators

Strings

Casting

How to find the maximum of N numbers

Python

Bubble sort

Matplotlib Plot

Python continue

da Cristina | Giu 12, 2021 | Python

Python continue statement allows us to stop the current iteration to start over from the first statement of the loop (for or while) in which it was entered.

Python continue – first example

So let’s take a simple example to better understand how it works.

We enter numbers, if the number is negative we use the continue statement to make it skip all the other lines of code and start again from the beginning.

Here is the simple program:

i = 0
while i <3:
   n = int(input('Insert a number: '))
   if n < 0:
       continue
   i += 1

In this case, therefore, if we insert a negative number, the counter is not incremented and the cycle continues to insert numbers until all 3 are positive.

Try the code in the online compiler that you will find at the following link: Python compiler online.

Python continue - second example

Let's take a second example of using the continue statement in Python.

We print numbers from 1 to 10, skipping the number 5.

Here, then, is an example with the for loop:

for i in range(1,11):
  if i == 5:
    continue
  print(i)

The output produced is this:

1
2
3
4
6
7
8
9
10

As we can see, the number 5 was not printed.

Python continue - third example

Let's take another example to better understand how this instruction works.

Print the numbers 1 to 10 by skipping multiples of 3.

Here is the sample code:

for i in range(1,11):
  if i % 3 == 0:
    continue
  print(i)

The output produced is as follows:

1
2
4
5
7
8
10
As we can see, the numbers 3, 6 and 9 were not printed.

Conclusion

In this short lesson we have explained how the continue statement works in Python through simple examples.

Some useful links

Python tutorial

Python Compiler

Install Python

Variables

Assignment operators

Strings

Casting

How to find the maximum of N numbers

How to use the math module

Bubble sort

Matplotlib Plot

Break Python

da Cristina | Giu 12, 2021 | Python

Break in loops in Python – In this lesson we will study how to use the break statement in loops. This instruction is useful when we want to terminate the loop following a condition and usually go to the next code.

The break statement in Python, like in many other programming languages, allows you to exit the for or while loop immediately.

Break can be used in all loops, even nested loops. If used in nested loops, only the loop it is placed in will be terminated and other loops will continue as normal.

Break Python – first example with while

Let’s take a practical example immediately, with while loop.

Enter numbers and add them. As soon as you enter a negative number, you exit the while loop.

Here is a possible implementation of the proposed algorithm.

i = sum = 0

while i < 10:
    n = int(input('Insert a number: '))
    if n < 0:
        break
   sum += n
   i += 1

print('Sum is: ', sum)

In this example as soon as we insert a negative number we immediately exit the loop without adding it. In fact, break causes the immediate exit from the while loop.

Try this example in the online compiler, which you can find at this link: Python compiler online.

Break Python – second example with for

Let’s do the same example using the for this time. Also this time we insert the break when a condition occurs.

So here is a possible implementation:

sum = 0
for i in range(10):
    n = int(input('Insert a number: '))
    if n < 0:
        break
   sum += n
print('Sum is: ', sum)

As we can see also this time, when we insert a negative number, we get out of the loop.

Break Python - third example with for nested

In this example we use the break only in the innermost loop. We enter as a condition, when i equals 1 and j equals 3.

So here is a possible example:

'''
Break Python - FOR LOOP Nested
'''
for i in range(1,3):
    for j in range(1,5):
        print(j, end = '')
        if j == 3 and i == 1:
          break
    print()

In this lesson we have made some examples of breaks in Python, in the next lesson we will talk about continues.

Some useful links

Python tutorial

Python Compiler

Install Python

Variables

Assignment operators

Strings

Casting

How to find the maximum of N numbers

How to use the math module

Bubble sort

Matplotlib Plot