Name:
Directions: Work only on this sheet (on both sides, if needed); do not turn in any supplementary
sheets of paper. There is actually plenty of room for your answers, as long as you organize yourself
BEFORE starting writing. In order to get full credit, SHOW YOUR WORK.
Several problems will ask you to present a “Pythonic” way of accomplishing a certain task.
The term, which is common in Python circles, simply means taking advantage of Python’s
features. Often it will mean that the task can be accomplished in a single line. It does not
mean that you are expected to always use the most esoteric Python feature (and certainly
not one which is outside the scope of our course materials), but it does mean that you should
make a reasonable attempt to make good use of the language.
1. (15) Write a Python code fragment which will create 5 files, named a1 through a5, i.e. open them for writing.
2. (20) The code below implements the ideas discussed in class, by which an integer could be converted to a 4-byte
“string” to transmit or store the integer compactly. Fill in the missing blanks:
def inttostring(n):
m=n
out = ’’
for i in range(4):
c=m%256
out += _____________
m /= 256
return out
def stringtoint(s):
m=0
for i in range(4):
m = ______________
return m
3. (15) Look at the handout on conversion to/from Roman numerals. Suppose romanNumeralMap had been
implemented as a dictionary rather than as a tuple of tuples, so that for instance one element would be ’M’:1000.
Show how the for loop in toRoman() would be rewritten.
4. (15) Suppose we have a list xwhich we want to rotate, i.e. the new x[0] will be the old x[1], the new x[1]
will be the old x[2], ..., and the new x[len(x)-1] will be the old x[0]. Write Pythonic code to do this (it must be
single-statement code for full credit).
5. (15) Suppose our source file x.py defines functions f,gand h. Elsewhere in the code, a call is to be made to one
of these functions (with no arguments), depending on what the user puts on the command line. For example, if the
user types
python x.py g
then the program will execute g. Write Pythonic code which makes the call (must be single-line code for full credit).
6. (20) TCP treats all bytes sent by a network node as collectively comprising one long message. In some applications,
though, we wish to send “records” of a given length, say 80 characters. A function which is supposed to read the next
record would start with whatever bytes had been “leftover” from before, and then read from the network until it had
obtained 80 bytes. For such applications, we might write a subclass of socket. It would have an instance variable
named incoming, and an instance function named getrec() with a single argument, reclength. The function
getrec() would return a string of length reclength (or an empty string, if we are at the end of the entire message),
which it would obtain by first removing bytes from incoming and calling recv() as necessary.
Write the function getrec(), in a short, Pythonic manner.
Solutions:
1.
f = []
1
