Description
Python Basics and Parsing with Python
Principles of Programming Languages
Solve the following problems in Python. Each problem is worth five (5) points
each. You may use regular expressions in your solutions to the problems.
Problem 1:
Write a program that reads a line via input() and determines if the input is a
legal identifier. The program should print only one output: True or False, and
then exit.
A Python identifier starts with a letter (A – Z, or a – z) or an
underscore (_), followed by zero or more letters, underscores, or digits (0 – 9).
Legal Python identifiers cannot be Python keywords. Python keywords are
reserved and so cannot be used as constants, variables, function names, class
names, or as any other identifier in Python.
Note: Starting an identifier with a single leading underscore indicates that
the identifier is private. Starting an identifier with two leading underscores
indicates a strongly private identifier. If the identifier also ends with two
trailing underscores, the identifier is a language-defined special name.
You are not permitted to use the following library methods for this problem:
-keyword.iskeyword()
-str.isidentifier()
The point of this problem is to work out how one would implement such a method
by manually parsing the input.
You can easily view a list of all Python keywords by using the built-in “help”
function.
——————————————————————————–
Python 3.5.2 (default, Nov 12 , 13:43:14)
[GCC 5.4.0 20160609] on linux
Type “help”, “copyright”, “credits” or “license” for more information.
>>> help()
Welcome to Python 3.5’s help utility!
If this is your first time using Python, you should definitely check out
the tutorial on the Internet at http://docs.python.org/3.5/tutorial/.
Enter the name of any module, keyword, or topic to get help on writing
Python programs and using Python modules. To quit this help utility and
return to the interpreter, just type “quit”.
To get a list of available modules, keywords, symbols, or topics, type
“modules”, “keywords”, “symbols”, or “topics”. Each module also comes
with a one-line summary of what it does; to list the modules whose name
or summary contain a given string such as “spam”, type “modules spam”.
help> keywords
Here is a list of the Python keywords. Enter any keyword to get more help.
False def if raise
None del import return
True elif in try
and else is while
as except lambda with
assert finally nonlocal yield
break for not
class from or
continue global pass
help>
——————————————————————————–
Problem 2:
Write a program that reads a line via input() and determines if it is a legal
number. The program should print only one output: int, float, or None and then
exit.
Your program must manually parse the inputs. Do not merely pass the strings to
the type conversion functions and catch the exceptions.
In Python 3, there is effectively no limit to how long an integer value can be.
Of course, it is constrained by the amount of memory your system has, as are all
things , but beyond that an interger can be as long as your need it to be. The
following strings can be prepended to an integer value to indicate a base other
than 10:
0b (zero + lowercase letter ‘b’) Base 2 (binary)
0B (zero + uppercase letter ‘B’) Base 2 (binary)
0o (zero + lowercase letter ‘o’) Base 8 (octal)
0O (zero + uppercase letter ‘O’) Base 8 (octal)
0x (zero + lowercase letter ‘x’) Base 16 (hexadecimal)
oX (zero + uppercase letter ‘X’) Base 16 (hexadecimal)
Values with these prefixes are legal numbers (integers) in Python.
The float type in Python designates a floating-point number. Float values are
specified with a decimal point.
https://docs.python.org/3/tutorial/floatingpoint.html
Optionally, the character ‘e’ or ‘E’ followed by a positive or negative integer
may be appended to specify scientific notation.
Example: 4.2e-4 = 0.00042
Float values are 64-bit “double-precision” values, according to IEEE 754
standard ( https://en.wikipedia.org/wiki/IEEE_754 ). In that case, the
maximum value a floating-point number can have is approximately 1.8 x 10^308.
Python will indicate a number greater than that by the string “inf”.
The closest a nonzero number can be to zero is approximately 5.0 x 10^-324.
Anything closer to zero than that is effectively zero.
Floating point numbers are represented internally as binary (base-2) fractions.
Most decimal fractions cannot be represented exactly as binary fractions, so in
most cases the internal representation of a floating-point number is an
approximation of the actual value. In practice, the difference between the
actual value and the represented value is very small and should not usually
cause significant problems.
Problem 3:
3. Write a program that reads two lines (two sequential calls to input()) and
then determines if the combined result is a legal string enclosed within single
or double quotes. The program should print only one output: True or False, and
then exit.
The following is a table of escape sequences which cause Python to suppress the
usual special interpretation of a character in a string:
\’ Literal single quote (‘) character
\” Literal double quote (“) character
\newline Terminates input line. Newline is ignored
\\ Literal backslash (\) character
To break up a string over more than one line, include a backslash before
each newline, and the newlines will be ignored:
>>> ‘a\
… bc’
‘abc’
Equiavlently for the assignment:
first input: ‘ab\
second input: c’
The result is the valid string: ‘abc’, and your program should output True.
Problem 4:
Write a program that reads a date in the format: MM/DD/YYYY, from the command
line and print it out as: Day, Month DD, Year. If the input is formatted
incorrectly, or if the input does not correspond to a valid date, then your
program should ouput: None.
Your program should first manually check that the input is formatted correctly.
You may only use methods from the datetime library to determine whether the
input is a valid date, and then produce the output string.
For example we read “02/07/2019′ and output “Thursday, Feburary 7, 2019”.
Submission Instructions:
1. Please write each program in a separate file.
2. The file name should correspond the problem for which your program is
written.
Example: Your program for problem 1 should be called “hw1p1.py”.
3. Please collect and submit your program files as a compressed zip file.
4. The title of the compressed file should be:
cse307_hw01_LastNameFirstName
5. This is an individual assignment. Any collaboration on writing your programs
will be treated as a violation of academic integrity.
