06_standard_library.md

The Python Standard Library

Python comes with many built-in modules that offer ready-to-use solutions to common programming problems. To use these modules, you must use the import keyword. Once imported in your Python script, you can use the functions provided by the module in your script.

We will use the built-in math module that allows us to use advanced mathematical functions.

import math

You can also import specific functions or constants from the module like below

from math import pi
print(pi)

Calculating Distance

Given 2 points with their Latitude and Longitude coordinates, the Haversine Formula calculates the straight-line distance in meters, assuming that Earth is a sphere.

The formula is simple enough to be implemented in a spreadsheet too. If you are curious, see my post about using this formula for calculating distances in a spreadsheet.

We can write a function that accepts a pair of origin and destination coordinates and computes the distance.

san_francisco = (37.7749, -122.4194)
new_york = (40.661, -73.944)

def haversine_distance(origin, destination):
  lat1, lon1 = origin
  lat2, lon2 = destination
  radius = 6371000
  dlat = math.radians(lat2-lat1)
  dlon = math.radians(lon2-lon1)
  a = math.sin(dlat/2) * math.sin(dlat/2) + math.cos(math.radians(lat1)) \
    * math.cos(math.radians(lat2)) * math.sin(dlon/2) * math.sin(dlon/2)
  c = 2 * math.atan2(math.sqrt(a), math.sqrt(1-a))
  distance = radius * c
  return distance

distance = haversine_distance(san_francisco, new_york)
print(distance/1000, 'km')

Discover Python Easter Eggs

Programmers love to hide secret jokes in their programs for gun. These are known as Easter Eggs. Python has an easter egg that you can see when you try to import the module named this. Try writing the command import this below.

import this

Let's try one more. Try importing the antigravity module.

Here's a complete list of easter eggs in Python.

Exercise

Find the coordinates of 2 cities near you and calculate the distance between them by calling the haversine_distance function below.

def haversine_distance(origin, destination):
  lat1, lon1 = origin
  lat2, lon2 = destination
  radius = 6371000
  dlat = math.radians(lat2-lat1)
  dlon = math.radians(lon2-lon1)
  a = math.sin(dlat/2) * math.sin(dlat/2) + math.cos(math.radians(lat1)) \
    * math.cos(math.radians(lat2)) * math.sin(dlon/2) * math.sin(dlon/2)
  c = 2 * math.atan2(math.sqrt(a), math.sqrt(1-a))
  distance = radius * c
  return distance

# city1 = (lat1, lng1)
# city2 = (lat2, lng2)
# call the function and print the result

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