Generate a set of random values based on seed

Question

I am a novice when it comes to Python. I am working stuff related to Flowshop scheduling and so to generate benchmarks I used one by Taillard (Link to his homepage). The details are in the technical report.

Since I ported the code from C which I am not really good at please review my Python script:

# Format - random seed, number of jobs, number of machines
# Use a separate file and precede comments with a # symbol

from numpy import int32
import math

problem = list()

# Generate a random number uniformly between low and high
def unif(seed, low, high):
    """This function generates a random number between low\
            and high based on seed
    Seed is implemented as static for set of random values based on a series\
            of seed values"""

    if getattr(unif, "seed_value",0) == 0 or unif.seed_value is None:
        #create attribute seed_value which is static for method unif
        unif.seed_value = seed #inititalization if attribute does not exist

    # constants for random number
    a = 16807
    b = 127773
    c = 2836
    m = 2**(31) - 1

    k = math.floor(unif.seed_value / b)

    unif.seed_value = int32(a * (unif.seed_value % b) - k * c)
    # use numpy 32 bit int
    if unif.seed_value < 0: # 32 bit int overflow
        unif.seed_value = unif.seed_value + m

    value_0_1 = unif.seed_value/float(m)

    return int(low + math.floor(value_0_1 * (high - low + 1))) # random\
            # number generated

# generates a problem for given number of machines and jobs in problem tuple
def generate_flow_shop(p, output):
    """Generates a flow shop problem set for a set in problem tuple and\
            writes to file in output"""
    time_seed = int(problem[p][0])
    d = list() # list containing the problem

    for i in range( int(problem[p][2]) ):
        line = list()

        line = [ unif(time_seed, 1, 99) for j in range(int(problem[p][1])) ]

        # for j in range(0, int(problem[p][1])):
        #     line.append(unif(time_seed, 1, 99))
        # 99 - max duration of op.
        d.append(line)
    unif.seed_value = None

    for line in d:
        datum = ' '.join(map(str,line))
        output.write("%s\n" % (datum))

def main():
    name = input("Enter filename to write the generated values:\n> ")
    seedfile = input("Enter filename of the seed values:\n> ")

    with open(seedfile) as in_file:
        for i in in_file:
            if line[0] == '#':
                continue
            else:
                line = i.strip().split()
                problem.append(tuple( map(int,line) ) )

    with open("%s" % (name), "w") as out_file:
        for i in range(0, len(problem)):
            out_file.write("%s %04d %s %s\n" %\
                           ("p", i, problem[i][1], problem[i][2]))
            generate_flow_shop(i, out_file)

if __name__ == '__main__':
    main()

The link to the original C program is here.

This is the link to the output which is the expected output ie. the code is actually correct.

The main purpose of this module is to generate a set of values that can be used to test our implemented solutions ie. it is a generated problem set but not completely random but reproducible if the seeds entered are the same.

Note: The seedfile is a file that contains the values that are defined in the struct problem in the C program.

What I mainly need feedback on are:

• Can the script be improved further with respect to use of Python idioms?
• Since the generated file should again be parsed as input for testing, is writing to a file and then opening it again to test the scripts the best way? Is the written file format the best one for parsing again as input?

Answer 1

• unif.seed_value is very un-Pythonic. Instead use a class.
• Rather than using getattr(unif, "seed_value",0), you can make self.seed_value at object instantiation, and use that as the default, unless it's falsy, where it'd instead use seed.
• math.floor is mostly the same as int. If you're using this on division, you can change it to floor divisions using //.
• numpy.int32 is odd, it adds a dependency to numpy that shouldn't be needed. Instead you can use & or %, this also means that it doesn't throw an error if the number is greater than (1 << 31) - 1.
• unif.seed_value/float(m) is the same as unif.seed_value/m in Python 3. In Python 2 it'd do floor division, unless one number is a float.
• generate_flow_shop shouldn't need to take output, that should be implemented in main.
• generate_flow_shop should take a single problem rather than the list of problems.
• You can use tuple unpacking to give all values in the problem a name.
• I heavily recommend str.format over the old % formatting operator. It has less bugs, and is enhanced in 3.6 with f-strings.
• You can use _ as a 'throw away variable' in Python, it's somewhat a standard and lets developers ignore that variable, greatly increasing readability.

unif uses some fairly odd math, and so I decided to go for a more succinct approach. And so I'd change your code to: (note, it's untested)

class Random:
    def __init__(self):
        self.seed_value = None

    def unif(self, seed, low, high):
        seed_value = self.seed_value or seed

        a = 16807
        b = 127773
        c = 2836
        m = (1 << 31) - 1

        seed_value = (a * (seed_value % b) - (seed_value // b) * c)

        self.seed_value = (seed_value + (seed_value < 0)) & m
        return int(low + self.seed_value / m * (high - low + 1))

    def generate_flow_shop(self, problem):
        """Generates a flow shop problem set for a set in problem tuple and\
                writes to file in output"""

        time_seed, num_jobs, num_mach = problem
        r = [
            [
                self.unif(time_seed, 1, 99)
                for _ in range(num_jobs)
            ]
            for _ in range(num_mach)
        ]
        self.seed_value = None
        return r


def main():
    name = input("Enter filename to write the generated values:\n> ")
    seedfile = input("Enter filename of the seed values:\n> ")
    r = Random()

    with open(seedfile) as in_file:
        problems = [
            tuple(map(int, line.strip().split()))
            for line in in_file
            if line[0] != "#"
        ]

    with open(name, "w") as out_file:
        for i, problem in enumerate(problems):
            out_file.write("p {0:04} {1[1]} {1[2]}\n".format(i, problem)))
            data = r.generate_flow_shop(problem)
            out_file.write(''.join(' '.join(line) + '\n' for line in data))


if __name__ == '__main__':
    main()

Answer 2

As far as styling goes- Triple quotation marks signifying a docstring end should be on a seperate line:

def func():
    """This docstring explains
        how the function should
        be used.
    """

Also, there is no need to escape newlines in docstrings. I suppose you could open the file in w+ or r+ mode (wr / rw);

with open(seedfile, "r+") as f:
    # magic