knerr cs21 notes...

back to schedule

WEEK01: intro to python, unix, cs21, interviews with students
---------------------------------------------------------------
 F: loops, range, sequences

Announcements:
  - Lab 1
  - 15-min interview with me

REVIEW of hello.py

name = raw_input("your full name: ")
yearborn = input("year you were born: ")

print "\nHello, " + name
age = 2009 - yearborn
print "You are " + str(age) + " years old!\n"

UNIX:
  - how to copy stuff from my inclass folder:

       cp /home/jk/inclass/hello.py hello.py
            or
       cp /home/jk/inclass/hello.py  .

  - how to start a new program:

       vim newprog.py

DEBUGGING:
  - try to break your programs and see what happens

LOOPS:

  for < var >  in < sequence >:
    do this
    and this
  but not this

  < var > is a variable you choose (i, x, foo, ch, etc)
  < sequence > is a special python set of values, which
    can be any of these:
         - a string of characters, like "Hello!!"
         - a list of integers, like [1,2,3,4,5]
         - a list of anything, like [1,"hi",5.6,"no]

  for loop examples:

>>> for ch in "hello":
...   print ch
... 
h
e
l
l
o

>>> for ch in "hello class":
...   print ch*5
... 
hhhhh
eeeee
lllll
lllll
ooooo
     
ccccc
lllll
aaaaa
sssss
sssss

>>> for i in [1,2,3,4,5]:
...   print "i = " + str(i)
... 
i = 1
i = 2
i = 3
i = 4
i = 5


  an easy way to create a list is with the range function:

>>> range(5)
[0, 1, 2, 3, 4]
>>> range(1,10)
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(1,20,2)
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

  and here's a for loop example using range:

>>> for i in range(20,1,-2):
...    print "----->" + str(i)
... 
----->20
----->18
----->16
----->14
----->12
----->10
----->8
----->6
----->4
----->2


---> can you write this program?

$ python blastoff.py 

countdown start: 7
 
. . . . 7
. . . . 6
. . . . 5
. . . . 4
. . . . 3
. . . . 2
. . . . 1
blastoff!!