MCS 275 Spring 2021
David Dumas
I expanded the written Python tour to include today's material:
Python tour (prep for MCS 275)
If you find something confusing or unfamiliar there, let me know and also check the textbook or the relevant MCS 260 slides.
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 Lec 23.