MCS 260 Fall 2021 Worksheet 9 Solutions¶

# Contents of terminal3.py

"""Mini terminal application for demonstration purposes"""
# MCS 260 Fall 2021 Lecture 21, 22, and Workseet 9

# This version of the terminal puts the commands and dispatch
# table in a separate module.

# Note: the os module import from terminal2.py is NOT needed 
# in this version, because os functions are only used in
# termcommands.py

import termcommands

# Main loop

while True:
    # Prompt for input
    s=input("? ")
    cmdparts = s.split()
    if len(cmdparts) == 0:
        print("No command given.")
        continue
    
    name = cmdparts[0]
    args = cmdparts[1:]
    if name in termcommands.handlers:
        try:
            termcommands.handlers[name](*args)
        except TypeError:
            print("Malformed command (wrong number of args?)")
    else:
        termcommands.do_unknown()

# Contents of termcommands.py

"""Commands and dispatch table for terminal3.py"""
# MCS 260 Fall 2021 Worksheet 9

import os   # needed because many command implementations call os functions!

# COMMANDS

def do_exit():
    """exit the program"""
    exit()

def do_unknown():
    print("Unknown or malformed command.  (The 'help' command will list known commands.)")

def do_help():
    """print a help message"""
    print("Known commands:")
    for name in handlers:
        print(name,"-",handlers[name].__doc__)

def do_whereami():
    """show current working directory"""
    print(os.getcwd())

def do_moveto(a):
    """change current working directory"""
    os.chdir(a)

def do_listdir(*args):
    """list the contents of a directory"""
    if len(args) > 1:
        raise TypeError("listdir accepts at most one argument")
    if len(args) == 1:
        a = args[0]
    else:
        a = os.getcwd()
    for fn in os.listdir(a):
        print(fn)

def do_numfiles(a):
    """show number of files and subdirs in a directory"""
    numfiles = 0
    numdirs = 0   # a might be "C:\Users\ddumas\Dropbox\teaching\mcs260\public\samplecode"
    for fn in os.listdir(a):
        if os.path.isfile(os.path.join(a,fn)):  # fn might be "map1.json"
            numfiles = numfiles + 1
        elif os.path.isdir(os.path.join(a,fn)):
            numdirs = numdirs + 1
    print("{} files\n{} dirs".format(numfiles,numdirs))

def do_create(a):
    """make a new empty file"""
    if os.path.exists(a):
        print("ERROR: {} already exists".format(a))
    else:
        # File does not exist; ok to create
        open(arg,"w").close()

def do_copy(src,dst):
    """copy contents of SRC to new file DST"""
    # copy the file named arg1 to a new file named arg2
    if os.path.exists(dst):
        print("ERROR: Refusing to overwrite existing file")
    else:
        # TODO: Replace with memory-efficient incremental copy
        infile=open(src,"rb")  # "b" means "even if it's not a text file"
        data=infile.read()
        infile.close()
        outfile=open(dst,"wb")
        outfile.write(data)
        outfile.close()

# DISPATCH TABLE

handlers = {
    "help": do_help,
    "exit": do_exit,
    "listdir": do_listdir,
    "numfiles": do_numfiles,
    "create": do_create,
    "moveto": do_moveto,
    "whereami": do_whereami,
    "copy": do_copy
}

# Save this as `example.py` if you want to test the counter program
"Sample of counting"
# MCS 260

def this_line_counts():  # I am a comment on a line that contains code
    "I am a docstring!"
    # TODO: Fix this!
    print("Hello.")

this_line_counts()

# content of commentzapper.py
# MCS 260 Fall 2021 Worksheet 9
import sys

fobj = open(sys.argv[1],"r",encoding="UTF-8")
for line in fobj:
    stripped = line.strip()
    if len(stripped)>0 and stripped[0] == "#":
        continue
    print(line,end="")

import json

# We assume "iterpuzzles.json" is in the CWD
fobj=open("iterpuzzles.json","r",encoding="UTF-8")
L=json.load(fobj)
fobj.close()

all( [ any( [w[0]=="e" for w in sublist ]) for sublist in L] )

L[6]

any( ["antipathy" in sublist for sublist in L ] )

awords=[]
for sublist in L:
    for w in sublist:
        if w not in awords and w[:4] == "anti":
            awords.append(w)
awords.sort()
print(awords)

len( [ sublist for sublist in L if len(sublist)%2 ] )

[ i for i,sublist in enumerate(L) if L[i][1][0]=="a" ]

L[77]

# MCS 260 Fall 2021 Worksheet 9

def single_letter(s):
    """If s is one letter, return it.  Otherwise raise ValueError."""
    if len(s) != 1:
        raise ValueError("Not a single letter: {}".format(s))
    return s
    
converters = {
    "float": float,
    "integer": int,
    "string": str,
    "letter": single_letter,
}

def multi_input(L):
    """Read multiple input values, based on a list of types given in `L`."""
    results = []
    for valtype in L:
        while True:
            s = input(valtype+": ")
            try:
                x = converters[valtype](s)
                break
            except Exception:
                print("That didn't work; expected entry of a {}.".format(valtype))

multi_input( ["float", "string", "integer", "letter"] )