[2021 spring] CS61A Lab 13: Regular Expressions, BNF

Lab 13： https://inst.eecs.berkeley.edu/~cs61a/sp21/lab/lab13/

目录

• Q2: Roman Numerals
• Q3: Calculator Ops
• Q4: CS Classes

Q2: Roman Numerals

注意'\b'的用法

def roman_numerals(text):
    """
    Finds any string of letters that could be a Roman numeral
    (made up of the letters I, V, X, L, C, D, M).

    >>> roman_numerals("Sir Richard IIV, can you tell Richard VI that Richard IV is on the phone?")
    ['IIV', 'VI', 'IV']
    >>> roman_numerals("My TODOs: I. Groceries II. Learn how to count in Roman IV. Profit")
    ['I', 'II', 'IV']
    >>> roman_numerals("I. Act 1 II. Act 2 III. Act 3 IV. Act 4 V. Act 5")
    ['I', 'II', 'III', 'IV', 'V']
    >>> roman_numerals("Let's play Civ VII")
    ['VII']
    >>> roman_numerals("i love vi so much more than emacs.")
    []
    >>> roman_numerals("she loves ALL editors equally.")
    []
    """
    return re.findall(r'\b([IVXLCDM]+)\b', text)

Q3: Calculator Ops

def calculator_ops(calc_str):
    """
    Finds expressions from the Calculator language that have two
    numeric operands and returns the expression without the parentheses.

    >>> calculator_ops("(* 2 4)")
    ['* 2 4']
    >>> calculator_ops("(+ (* 3 (+ (* 2 4) (+ 3 5))) (+ (- 10 7) 6))")
    ['* 2 4', '+ 3 5', '- 10 7']
    >>> calculator_ops("(* 2)")
    []
    """
    return re.findall(r'[+*-/]\s[0-9]+\s[0-9]+', calc_str)

Q4: CS Classes

def cs_classes(post):
    """
    Returns strings that look like a Berkeley CS class,
    starting with "CS", followed by a number, optionally ending with A, B, or C.
    Case insensitive.

    >>> cs_classes("Is it unreasonable to take CS61A, CS61B, CS70, and EE16A in the summer?")
    True
    >>> cs_classes("how do I become a TA for cs61a? that job sounds so fun")
    True
    >>> cs_classes("Can I take ECON101 as a CS major?")
    False
    >>> cs_classes("Should I do the lab lites or regular labs in EE16A?")
    False
    """
    return bool(re.search('[Cc][Ss][0-9]+[ABCabc]*', post))