Chapter 16. Functional Programming
Description: Python from novice to pro
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## Chapter 16. Functional Programming

## 16.1. Diving in

In Chapter 13, Unit Testing, you learned about the philosophy of unit testing. In Chapter 14, Test-First Programming, you stepped through the implementation of basic unit tests in Python. In Chapter 15, Refactoring, you saw how unit testing makes large-scale refactoring easier. This chapter will build on those sample programs, but here we will focus more on advanced Python-specific techniques, rather than on unit testing itself.

The following is a complete Python program that acts as a cheap and simple regression testing framework. It takes unit tests that you've written for individual modules, collects them all into one big test suite, and runs them all at once. I actually use this script as part of the build process for this book; I have unit tests for several of the example programs (not just the `roman.py` module featured in Chapter 13, Unit Testing), and the first thing my automated build script does is run this program to make sure all my examples still work. If this regression test fails, the build immediately stops. I don't want to release non-working examples any more than you want to download them and sit around scratching your head and yelling at your monitor and wondering why they don't work.

### Example 16.1. `regression.py`

If you have not already done so, you can download this and other examples used in this book.

    """Regression testing framework

    This module will search for scripts in the same directory named
    XYZtest.py.  Each such script should be a test suite that tests a
    module through PyUnit.  (As of Python 2.1, PyUnit is included in
    the standard library as "unittest".)  This script will aggregate all
    found test suites into one big test suite and run them all at once.
    """

    import sys, os, re, unittest

    def regressionTest():
        path = os.path.abspath(os.path.dirname(sys.argv[0]))
        files = os.listdir(path)
        test = re.compile("test\.py$", re.IGNORECASE)
        files = filter(test.search, files)
        filenameToModuleName = lambda f: os.path.splitext(f)[0]
        moduleNames = map(filenameToModuleName, files)
        modules = map(__import__, moduleNames)
        load = unittest.defaultTestLoader.loadTestsFromModule
        return unittest.TestSuite(map(load, modules))

    if __name__ == "__main__":
        unittest.main(defaultTest="regressionTest")

Running this script in the same directory as the rest of the example scripts that come with this book will find all the unit tests, named ``module`test.py`, run them as a single test, and pass or fail them all at once.

### Example 16.2. Sample output of `regression.py`

    [you@localhost py]$ python regression.py -v
    help should fail with no object ... ok
    help should return known result for apihelper ... ok
    help should honor collapse argument ... ok
    help should honor spacing argument ... ok
    buildConnectionString should fail with list input ... ok
    buildConnectionString should fail with string input ... ok
    buildConnectionString should fail with tuple input ... ok
    buildConnectionString handles empty dictionary ... ok
    buildConnectionString returns known result with known input ... ok
    fromRoman should only accept uppercase input ... ok
    toRoman should always return uppercase ... ok
    fromRoman should fail with blank string ... ok
    fromRoman should fail with malformed antecedents ... ok
    fromRoman should fail with repeated pairs of numerals ... ok
    fromRoman should fail with too many repeated numerals ... ok
    fromRoman should give known result with known input ... ok
    toRoman should give known result with known input ... ok
    fromRoman(toRoman(n))==n for all n ... ok
    toRoman should fail with non-integer input ... ok
    toRoman should fail with negative input ... ok
    toRoman should fail with large input ... ok
    toRoman should fail with 0 input ... ok
    kgp a ref test ... ok
    kgp b ref test ... ok
    kgp c ref test ... ok
    kgp d ref test ... ok
    kgp e ref test ... ok
    kgp f ref test ... ok
    kgp g ref test ... ok

    ----------------------------------------------------------------------
    Ran 29 tests in 2.799s

    OK

| The first 5 tests are from `apihelpertest.py`, which tests the example script from Chapter 4, The Power Of Introspection.
| The next 5 tests are from `odbchelpertest.py`, which tests the example script from Chapter 2, Your First Python Program.
| The rest are from `romantest.py`, which you studied in depth in Chapter 13, Unit Testing.