Williams College Lecture 5 Brent Heeringa, Bill Jannen
Review
Everything in python is an object that has an associated type. You can always find out the type of an object by using
the type function. There are many builtin types in Python. We’ve already seen int,float, and str. There is a
boolean type bool that has only two values True and False. There is also a NoneType called None, which we
will talk about more later.
Recall the built-in functions below:
•int(x) : construct an integer from some object x, which is usually has type integer, float, or string.
•str(x) : construct a string representation of some object x.
•float(x): construct a float from some object x, which is usually has type integer, float, or string.
Modules and Packages
Amodule is a file containing Python code—function definitions, expressions, and statements. Modules provide a
way to logically group collections of related code, keep the global namespace clear, and distribute code to others.
By using the statement
import mymodule
we are letting python know that there is a file called mymodule.py somewhere in the Python search path that
contains functions about which we care. We can now access these functions using the dot notation. For example, if
mymodule.py contains the function hipper chatter then we can call it with
mymodule.hipper_chatter
Python Script Mode
Let’s write a program called sum.py that takes two arguments from the command line and prints out their sum.
import sys
x = sys.argv[1]
y = sys.argv[2]
print(‘‘The sum of’’+x+‘‘and ’’+y+‘‘is ’’ + (x+y))
First some explanation. The import command tells Python to include a bundle of code, called a module, in
our program. Importing a module gives us access the variables and functions it defines. The module sys gives us
access to a variable called argv, which is a vector of strings that appear on the command line. sys.argv[0] is
the name of the script. sys.argv[1] is the first argument, sys.argv[2] is the second argument, and so on.
Let’s run this script in script mode.
$ python3 sum.py 5 6
The sum of 5 and 6 is 56
Um, that’s not right. What’s wrong? The arguments are strings of characters, not numbers.
import sys
x = int(sys.argv[1])
y = int(sys.argv[2])
print(”The sum of ” + str(x) + ” and ” + str(y)+”is”+str(x+y))
Fall Semester 2016 1 CS 135: Diving into the Deluge of Data
