MCS 275 Spring 2022
David Dumas
Expanded version of the code from the last two lectures:
The first non-comment statement in any Python file should be a string on a line by itself. That string should describe the file. It is called a docstring.
Docstrings can also appear as the first statement inside a function body or class definiton.
Anywhere else you want to put explanatory text, use a comment.
def divisble_by_7(x):
"""Return True if x is divisible by 7""" # <-- docstring!
return x % 7 == 0
# ... and then later ...
if divisible_by_7(10987654321):
print("Hey, did you know 10987654321 is a multiple of 7?!")
*It is also possible to define unnamed (anonymous) functions using lambda, but that isn't discussed in this quick overview.
A module keeps a bunch of related code in one place; good for reuse and organization. The statement
import modulenamewill look for modulename.py in current directory, or a built-in module with that name, and make its functions, classes, etc. available.
Use modulename.funcname(...) to call a function in a module.
See Lutz, Chapters 22-23 or MCS 260 Lec 20.
Classes let you define custom types in Python with attributes (data) and methods (behavior).
class Point:
"""A point in the xy-plane""" # <--- Remember docstring!
def __init__(self,x,y):
"""Initialize new point instance"""
self.x = x # make a new attribute (self.x)
self.y = y # make a new attribute (self.y)
def translate(self,dx,dy):
"""Move the point by a vector (dx,dy)"""
self.x += dx
self.y += dy
P = Point(1,2) # calls __init__(...)
P.translate(5,0)
print("After moving, P.x is",P.x) # will print 6
See Lutz, Chapters 27-28 and MCS 260 Lectures 25, 26, 27, 28.