Python Learning

pythonLearning.py

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#Here are some codes I wrote in python for learning
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# A prefix Calculator
import prefixCalclulator
prefixCalclulator.test()

prefixCalclulator.py

import sys
import unittest

# main calculate function, input is line of prefix expresssion
def calculate(line):
    # the set of operators supported
    operator_set = set(['+', '/', '*'])
    # a function to apply the operators
    operator_func = {
              '*': lambda pair: pair[0] * pair[1],
              '+': lambda pair: pair[0] + pair[1],
              '/': lambda pair: pair[0] / pair[1]}
    def apply_operator(operator, operand_1, operand_2):
        return operator_func[operator]((operand_1, operand_2))
    # begin the computing
    chars = line.split()
    operand_stack = []
    while len(chars) != 0:
        op = chars.pop()
        if op in operator_set:
            res = None
            try:
                res = apply_operator(op, operand_stack.pop(), operand_stack.pop())
            except Exception as e:
                raise Exception("Error in applying the operater '%s', because %s." % (op, e.args))
            #put back the result
            operand_stack.append(res)
        else:
            try:
                operand_stack.append(float(op))#prepare for division
            except Exception as e:
                raise Exception("Error in reading operand(operator) '%s', because %s . " % (op,str(e.args)) )
    return int(operand_stack[0])


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# read file and calculate each line
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if __name__ == "__main__":
    # check the cmd paras
    if len(sys.argv) > 1:
        file_name = sys.argv[1]
    else:
        raise Exception("No filename given!")
    # calculate the file
    try:
        with open(file_name, 'r') as f:
            for line in f:
                try:
                    print(calculate(line))
                except Exception as e:
                    print(str(e) + " Fail to calculate line: '%s'." % line.strip())
    except IOError:
        raise Exception("Reading file '%s' failed!" % file_name)

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# Unit Test for function
########################
class PrefixCalculatorTest(unittest.TestCase):
    def test_easy(self):
        self.assertEqual(calculate("* + 2 3 4"), 20)

    def test_onlyOperand(self):
        self.assertEqual(calculate("1"), 1)

    def test_devide(self):
        self.assertEqual(calculate("/ + 10 10 2"), 10)

    def test_devideFloat(self):
        self.assertEqual(calculate("* / 3 2 2"), 3)

def test():
    suite = unittest.TestLoader().loadTestsFromTestCase(PrefixCalculatorTest)
    unittest.TextTestRunner(verbosity=2).run(suite)