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Built-in Functions | Functions
Introduction to Python

Built-in Functions

What if you were asked to find the largest number in a list? With the knowledge you've gained, you could write a loop to check if the current element is larger/smaller than the previous biggest one and update it; if not, you'd continue. But for long lists, this method can be quite time-consuming. Thankfully, there are built-in functions that can make this task more efficient. Here are a few:

  • min(x, y, ...) - Returns the smallest value among x, y, ...;
  • max(x, y, ...) - Returns the largest value among x, y, ...;
  • abs(x) - Gives the absolute value of x;
  • round(x, n) - Rounds the number x to n decimal places;
  • pow(x, n) - Raises x to the power of n.

For instance, suppose we want to calculate the population density for a set of countries in the countries list. To do this, we'd divide the population by the area. Here's how it's done:

Code Description
  • countries = ...: This line creates a list named countries. Each item in this list is another list containing three elements: the name of a country, its area in square kilometers, and its population.


  • for i in range(len(countries)):: This starts a loop. len(countries) counts how many items are in the countries list, and range(len(countries)) creates a sequence of numbers from 0 up to (but not including) the number of items in the countries list. The variable i takes each of these numbers in turn as the loop runs.

  • if type(countries[i]) is list:: This line checks if each item (indexed by i) in the countries list is a list. In this code, every item will indeed be a list (containing the country details), so this condition will always be true.

  • pop_dens = countries[i][2]/countries[i][1]: Inside the loop, this line calculates the population density of each country. countries[i] accesses the i-th item in the countries list (which is one of the inner lists representing a country). countries[i][2] gets the population of the country (the third element in its list), and countries[i][1] gets the area of the country (the second element in its list). Dividing the population by the area gives the population density.

  • print(countries[i][0], pop_dens, 'people per km²'): This line prints three things:
  • 1. countries[i][0]: The first element in the i-th list of countries, which is the name of the country.
    2. pop_dens: The population density calculated in the previous step.
    3. 'people per km²': A string that just adds some context to the printed population density value.

    In the example above, our list had 5 nested sub-lists. We looped through the main list and checked if each item was a list. If it was, we divided the third item (population) by the second item (area).

    However, the results were not very reader-friendly since they had more than 10 decimal places. To make them more readable, we can use the round() function to reduce them to just 2 decimal places. Remember, this function takes two arguments: the first is the number you want to round, and the second specifies how many decimal places you want to keep.

    Code Description
  • countries = ...: This line initializes a list named countries. Each element within this list is another list that contains information about a country: the country's name, its land area in square kilometers, and its population.


  • The for loop, for i in range(len(countries)):: This line sets up a loop that will execute once for each element in the countries list. len(countries) counts how many elements are in the countries list, and range(len(countries)) generates a sequence of numbers from 0 to one less than the number of elements in the countries list. The variable i sequentially takes on each value in this range.

  • Inside the loop, if type(countries[i]) is list: checks whether each element accessed by countries[i] is a list. Given the structure of our countries list, this condition will always be true.

  • pop_dens = round(countries[i][2]/countries[i][1], 2): This line calculates the population density for the country at the current index i by dividing the population (third element, index 2) by the land area (second element, index 1). The round function is used to round the resulting population density to two decimal places.

  • print(countries[i][0], pop_dens, 'people per km²'): This command prints the name of the country (first element, index 0 of countries[i]), followed by the calculated population density (pop_dens), and the string 'people per km²'. This output gives a clear and formatted display of the population density for each country listed in the countries array.
  • As you can see, the revised result is much clearer and easier to understand.

    ¿Todo estuvo claro?

    Sección 6. Capítulo 1
    course content

    Contenido del Curso

    Introduction to Python

    Built-in Functions

    What if you were asked to find the largest number in a list? With the knowledge you've gained, you could write a loop to check if the current element is larger/smaller than the previous biggest one and update it; if not, you'd continue. But for long lists, this method can be quite time-consuming. Thankfully, there are built-in functions that can make this task more efficient. Here are a few:

    • min(x, y, ...) - Returns the smallest value among x, y, ...;
    • max(x, y, ...) - Returns the largest value among x, y, ...;
    • abs(x) - Gives the absolute value of x;
    • round(x, n) - Rounds the number x to n decimal places;
    • pow(x, n) - Raises x to the power of n.

    For instance, suppose we want to calculate the population density for a set of countries in the countries list. To do this, we'd divide the population by the area. Here's how it's done:

    Code Description
  • countries = ...: This line creates a list named countries. Each item in this list is another list containing three elements: the name of a country, its area in square kilometers, and its population.


  • for i in range(len(countries)):: This starts a loop. len(countries) counts how many items are in the countries list, and range(len(countries)) creates a sequence of numbers from 0 up to (but not including) the number of items in the countries list. The variable i takes each of these numbers in turn as the loop runs.

  • if type(countries[i]) is list:: This line checks if each item (indexed by i) in the countries list is a list. In this code, every item will indeed be a list (containing the country details), so this condition will always be true.

  • pop_dens = countries[i][2]/countries[i][1]: Inside the loop, this line calculates the population density of each country. countries[i] accesses the i-th item in the countries list (which is one of the inner lists representing a country). countries[i][2] gets the population of the country (the third element in its list), and countries[i][1] gets the area of the country (the second element in its list). Dividing the population by the area gives the population density.

  • print(countries[i][0], pop_dens, 'people per km²'): This line prints three things:
  • 1. countries[i][0]: The first element in the i-th list of countries, which is the name of the country.
    2. pop_dens: The population density calculated in the previous step.
    3. 'people per km²': A string that just adds some context to the printed population density value.

    In the example above, our list had 5 nested sub-lists. We looped through the main list and checked if each item was a list. If it was, we divided the third item (population) by the second item (area).

    However, the results were not very reader-friendly since they had more than 10 decimal places. To make them more readable, we can use the round() function to reduce them to just 2 decimal places. Remember, this function takes two arguments: the first is the number you want to round, and the second specifies how many decimal places you want to keep.

    Code Description
  • countries = ...: This line initializes a list named countries. Each element within this list is another list that contains information about a country: the country's name, its land area in square kilometers, and its population.


  • The for loop, for i in range(len(countries)):: This line sets up a loop that will execute once for each element in the countries list. len(countries) counts how many elements are in the countries list, and range(len(countries)) generates a sequence of numbers from 0 to one less than the number of elements in the countries list. The variable i sequentially takes on each value in this range.

  • Inside the loop, if type(countries[i]) is list: checks whether each element accessed by countries[i] is a list. Given the structure of our countries list, this condition will always be true.

  • pop_dens = round(countries[i][2]/countries[i][1], 2): This line calculates the population density for the country at the current index i by dividing the population (third element, index 2) by the land area (second element, index 1). The round function is used to round the resulting population density to two decimal places.

  • print(countries[i][0], pop_dens, 'people per km²'): This command prints the name of the country (first element, index 0 of countries[i]), followed by the calculated population density (pop_dens), and the string 'people per km²'. This output gives a clear and formatted display of the population density for each country listed in the countries array.
  • As you can see, the revised result is much clearer and easier to understand.

    ¿Todo estuvo claro?

    Sección 6. Capítulo 1
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