DataCamp.com — Python w/Data Science Track Ch 3: Packages

Packages

Directories of Python script.
Each script is a module that specify methods, functions, Python types aimed at solving problems.
Thousands of packages. Not all available in Python by default.
get-pip.py to install packages

Import statement to import entire package

Can import package like Numpy as:

import numpy
array([1, 2, 3])

#more standard/ preferred
import numpy as np
np. array([1, 2, 3])

from numpy import array
array([1, 2, 3])

Import package

As a data scientist, some notions of geometry never hurt. Let’s refresh some of the basics.

For a fancy clustering algorithm, you want to find the circumference, C, and area, A, of a circle. When the radius of the circle is r, you can calculate C and A as:

C=2πr
A=πr2

To use the constant pi, you'll need the math package. A variable r is already coded in the script. Fill in the code to calculate C and A and see how the print() functions create some nice printouts.

Instructions100

• Import the math package. Now you can access the constant pi with math.pi.
• Calculate the circumference of the circle and store it in C.
• Calculate the area of the circle and store it in A.

# Definition of radius
r = 0.43

# Import the math package
import math
from math import pi

# Calculate C
C = 2 * pi * r

# Calculate A
A = pi * pow(r, 2)

# Build printout
print("Circumference: " + str(C))
print("Area: " + str(A))

Selective import

General imports, like import math, make all functionality from the math package available to you. However, if you decide to only use a specific part of a package, you can always make your import more selective:

from math import pi

Let’s say the Moon’s orbit around planet Earth is a perfect circle, with a radius r (in km) that is defined in the script.

Instructions

• Perform a selective import from the math package where you only import the radians function.
• Calculate the distance travelled by the Moon over 12 degrees of its orbit. Assign the result to dist. You can calculate this as r * phi, where r is the radius and phi is the angle in radians. To convert an angle in degrees to an angle in radians, use the radians() function, which you just imported.

# Definition of radius
r = 192500

# Import radians function of math package
from math import radians

# Travel distance of Moon over 12 degrees. Store in dist.
dist = r * radians(12)

# Print out dist
print(dist)