Download Introduction to Python

New York University
School of Continuing and Professional Studies
Division of Programs in Information Technology
Introduction to Python
Homework, Session 9
EXERCISES
Ex. 9.1 Write a function callme that prints "function called…" every time you call it. Call the
function with the following code:
callme()
callme()
callme()
Expected output:
function called...
function called...
function called...
Ex. 9.2 Write a function printupper that takes one argument, a string, a prints that string
uppercased. Call it with the following code:
printupper('hello')
printupper('my you are loud')
printupper('I am not loud. You are.')
Expected output:
HELLO
MY YOU ARE LOUD
I AM NOT LOUD. YOU ARE.
Ex. 9.3 Write a function addme that takes two arguments, adds them together and returns
the two arguments added / concatenated. Call it thusly:
x = addme(4, 5)
print x
y = addme('hey', 'you')
print y
Expected output:
9
heyyou
Ex. 9.4 Write a function printlist that takes a list and loops through and prints each element
of the list. Call it thusly:
printlist([1, 2, 'a', 'b'])
Expected output:
1
2
a
b
Ex. 9.5 Create a module file named yourname.py where yourname is your first name. Do
not put a shebang (!#) line at the top.
Create a def hello: function (that prints hello, world!) inside the yourname.py
module.
Now in the same directory where you saved the module, create a python script. In
the script have an import yourname statement, and then call the function through the
module: yourname.hello()
Save the file and then run it.
Expected calls and output:
import yourname
yourname.hello()
# hello, world!
Ex. 9.6 Modify the above function to include an optional argument. If name=[something],
print hello, [something]! instead of hello, world! But if the name= parameter is not
passed, revert to saying hello, world!
So your def hello function code will be modified to accept the name=text argument
(i.e., def hello(name=False)), and then test to see if text has a value -- if it is True
(i.e., if name: is True). If it is True, print it after 'hello, '. If it doesn't, print 'hello,
world!'
Expected calls and output:
import yourname
yourname.hello()
yourname.hello(name='Python')
# hello, world!
# hello, Python!
Ex. 9.7 Create a function getlines(filename) that takes a filename, opens the file for that
filename, copies the lines of the file (i.e., from readlines()) to a list variable, and then
returns the list. In the calling code, call the function with a known filename, and
assign the return value of the call to a variable. Loop through the variable (of course
it is a list) and print out each line in the file.
Expected calls and output:
lines = getlines('testfile.txt')
for line in lines:
print line
# prints each line in file
HOMEWORK
9.1 Create a module called filelib.py that has three functions:
def getlines(filename, newlines=False): takes a filename, opens it and returns the lines
from the file, each stripped of any newline at the end. If newlines=True, the newlines will
not be removed. Remember to close the file before returning.
def gettext(filename): takes a filename, opens it and returns a string that contains the
text of the file.
def getfields(filename, delimiter=None): takes a filename, opens it and returns a list of
lists in which each list is a line from the file, split on the delimiter (for example, the module
will split on a comma if the comma is passed as delimiter). If delimiter is not passed, the
function splits on whitespace (i.e., the default behavior of split()). Make sure that the final
element of each line (or the line itself) is strip()ped. If a delimeter is passed that cannot
be found in any one of the lines, raise a ValueError exception with a message indicating
the problem.
Save your functions in a file called filelib.py and save it in a folder, for example your
python_scripts directory.
Now create a test Python script with the following code:
#!/usr/bin/env python
import filelib
data_file = '../python_data/student_db.txt'
lines = filelib.getlines(data_file, newlines=True)
print len(lines)
text = filelib.gettext(data_file)
print len(text)
# when the below line is uncommented, your module should raise a
# ValueError exception and, in the raised error, explain that the
# delimeter does not appear to be in the file. See the slide on
# raise (not covered in our class discussion) for details on raising an error
with message.
#list_of_lists = filelib.getfields(data_file, delimiter='baddelimeter')
list_of_lists = filelib.getfields(data_file, delimiter=':')
print list_of_lists
Expected output:
8
332
[['id','address','city','state','zip'], ['jk43','23 Marfield
Lane','Plainview','NY','10023'], ['ZXE99','315 W. 115th Street, Apt. 11B','New
York','NY','10027'], ['jab44','23 Rivington Street', Apt. 3R','New
York','NY','10002'], ['ak9','234 Main Street','Philadelphia','PA','08990'],
['ap172','19 Boxer Rd.','New York','NY','10005'], ['JB23','115 Karas
Dr.','Jersey City','NJ','07127'], ['jb29','119 Xylon Dr.','Jersey
City','NJ','07127']]