Exercise file: 2-bmi.py
The script is designed to calculate body mass index or BMI.
This script sets the variables weight and height using the user's input. The user's input is first converted to floating point numbers using the float function.
The height is converted from cm to m2 using the following formula:
height = (height/100)2
The body mass index (bmi) is then calculated and returned using the following formula:
bmi = weight/height
The function then returns bmi formatted to two decimal places using the round function.
Exercise file: 3-secondstring.py
The script is designed to take a sentence the user inputs, turn it backwards and take only every second letter starting from the last character and ending with the first one. So, for instance, "Backwards" becomes "srwc"
This script sets the variable input_string using the user's input. The input is first converted to a string using the str function.
The output_string variable is set using a slice of the string input_string. The slice goes from the last letter to the first letter in steps of 2 backwards.
The resulting string output_string is printed to the screen using the print function.
Exercise file: 4-collatz.py
This script is designed to take a positive integer and either divide it by two if it is even or multiply it by three and add 1 otherwise. In either case the result is printed to the screen. This continues until the positive integer becomes 1.
This script sets the variable any_pos_int using the user's input. The input is first converted to an integer using the int function.
The script runs an if statement which runs as follows:
If any_pos_int is not an integer, the user is informed using the print function which prints a warning to the screen. If any_pos_int is an integer then any_pos_int is printed to the screen with a blank space afterwards and a while loop is run.
This loop terminates if any_pos_int becomes equal to 1. In the loop, it checks whether any_pos_int divides evenly into 2 (i.e., is an even number). If it does, it divides any_pos_int by 2 and converts it to an integer using the int function. If it does not divide evenly into 2, then any_pos_int is trebled and 1 is added to the result, which is then converted to an integer.
Before the loop terminates any_pos_int is printed to the screen with a blank space afterwards.
Exercise file: 5-weekday.py
This script uses the datetime class in python to get the current day as a number between 0 and 6 and then tells the user whether that corresponds to a weekday or not.
Two lists are created which contain integers from 0-4 and 5-6. These correspond to weekdays (where 0 is Monday and 4 is Friday) and weekend days (5 is Saturday and 6 is Sunday).
The today and weekday functions in the datetime class are used to get the current date and then convert that date into a number betwen 0 and 6, which indicates what day it is in the week.
The programme then uses an if statement to check whether that is in the weekday list or the weekend day list. If it is the former, then it prints "Yes, unfortunately today is a weekday." Otherwise, it prints "It is the weekend, yay!"
Exercise file: 6-squareroot.py
This script takes input from the user, converts it to a floating-point number and gets the absolute value of it so that strings and non-positive numbers will be rejected. The result is set as the variable pos.
The pos variable is used as the first argument for the newton_root function from the module functions (described in the functions.py section at the bottom of this file).
The newton_root function will find the approximate square root for pos. The second argument is the number of iterations for which the newton_root function will run, in this case 10.
The result is rounded to 1 decimal place using the round function and set as the variable result
This string is then printed to the screen: "The square root of pos is approx. ". result is printed to the screen directly after this string.
Exercise file: 7-es.py
This script takes input from the command line to specify a file to be opened. When it opens the file, it goes through the file character by character and counts how many "e"'s (lower case e's) are present in the text file.
This script uses the sys module so that it can take an argument from the command line as an input variable, which is called sys.argv[1] (i.e., the second element of the array of input arguments, the first one being 7-es.py). This input variable is the string which designates which file is to be opened by a script. A test file is created with 6 "e"'s in total called "e.txt" (moby-dick.txt is also present for testing, it returns correct number of 'e's)
The function is called by entering "python 7-es.py e.txt" in this instance. The open function is used to open the file and each line is saved to a file object. This file object is composed of a series of strings, each string representing each line of the text document that is opened.
A for loop is used to iterate through each line (called line) of the text document. Another for loop iterates through each character (called ch) of the text document. A variable called ecount (which is set to 0 at the start of the script) is incremented every time the ch matches the character 'e' using an if statement.
At the end of the script, ecount is output to the screen using the print function.
Exercise file: 8-plots.py
The script imports the numpy module and the pyplot package (from the module matplotlib) using import.
A numpy array is created using the linspace function and is set as x. This array goes from a minimum of 0 and a maximum of 4 in steps of 0.0816 (i.e., 4/49).
The numpy arrays x, x2 and x3 are plotted on the same axes using the function plot taken from the the matplotlib.pyplot package. They are given appropriate labels, distinct colors, markers and line dashing so they can be differentiated.
A legend is added to the plot and the show function from pyplot is used to output the plot to the screen.
newton_root(input, iterations)
This function gets the square root of the variable input and employs the Newton-Raphson method for finding approximate roots to the following equation:
f(x) = x2-input.
This is identical to approximating the square root of input. The formula employed for the Newton-Raphson method in its general form is:
xn+1 = xn - f(x0)/f'(xn)
...where xn is the nth approximation, x0 is the initial guess, f(x0) is the function f at the intial guess, f'(xn) is the derivative of the function at the nth approximation. In this case:
f'(x) = 2x
To get an initial guess for the Newton-Raphson method, input is divided by 4 and set as the variable init. c The Newton-Raphson method is employed for iterations number of iterations using the following formula in a while loop:
init = init -((init2 - input)/(2 init))
The while loop will terminate when iterations number of iterations has been reached.
The function then returns init which is the approximate square root of input