quant-econ Solutions: More Language Features

Solutions for http://quant-econ.net/python_advanced_features.html

Exercise 1

Here's the standard solution



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def x(t):
    if t == 0:
        return 0
    if t == 1:
        return 1
    else:
        return x(t-1) + x(t-2)

Let's test it



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print [x(i) for i in range(10)]









    



[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

Exercise 2

One solution is as follows



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def column_iterator(target_file, column_number):
    """A generator function for CSV files.
    When called with a file name target_file (string) and column number 
    column_number (integer), the generator function returns a generator 
    which steps through the elements of column column_number in file
    target_file.
    """
    f = open(target_file, 'r')
    for line in f:
        yield line.split(',')[column_number - 1]
    f.close()

dates = column_iterator('test_table.csv', 1) 

i = 1
for date in dates:
    print date
    if i == 10:
        break
    i += 1

Exercise 3

Let's save the data first



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%%file numbers.txt
prices
3
8

7
21









    



Writing numbers.txt



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f = open('numbers.txt')

total = 0.0 
for line in f:
    try:
        total += float(line)
    except ValueError:
        pass

f.close()

print total



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