Python Unit testing

26.2. doctest — Test interactive Python examples

The doctest module searches for pieces of text that look like interactive Python sessions, and then executes those sessions to verify that they work exactly as shown. There are several common ways to use doctest:
• To check that a module’s docstrings are up-to-date by verifying that all interactive examples still work as documented.
• To perform regression testing by verifying that interactive examples from a test file or a test object work as expected.
• To write tutorial documentation for a package, liberally illustrated with input-output examples. Depending on whether the examples or the expository text are emphasized, this has the flavor of “literate testing” or “executable documentation”.


26.2.1. Simple Usage: Checking Examples in Docstrings

The simplest way to start using doctest (but not necessarily the way you’ll continue to do it) is to end each module M with:
if __name__ == "__main__":
    import doctest
    doctest.testmod()

Running the module as a script causes the examples in the docstrings to get executed and verified:
python M.py

26.2.2. Simple Usage: Checking Examples in a Text File

Another simple application of doctest is testing interactive examples in a text file. This can be done with the testfile() function:
import doctest
doctest.testfile("example.txt")
That short script executes and verifies any interactive Python examples contained in the file example.txt. The file content is treated as if it were a single giant docstring; the file doesn’t need to contain a Python program!

As with testmod(), testfile() won’t display anything unless an example fails. If an example does fail, then the failing example(s) and the cause(s) of the failure(s) are printed to stdout, using the same format as testmod().
By default, testfile() looks for files in the calling module’s directory. See section Basic API for a description of the optional arguments that can be used to tell it to look for files in other locations.
Like testmod(), testfile()‘s verbosity can be set with the -v command-line switch or with the optional keyword argument verbose.

26.2.3.1. Which Docstrings Are Examined?

The module docstring, and all function, class and method docstrings are searched. Objects imported into the module are not searched.

26.2.3.2. How are Docstring Examples Recognized?

In most cases a copy-and-paste of an interactive console session works fine, but doctest isn’t trying to do an exact emulation of any specific Python shell.

26.2.3.5. Option Flags

A number of option flags control various aspects of doctest’s behavior. Symbolic names for the flags are supplied as module constants, which can be or’ed together and passed to various functions. The names can also be used in doctest directives.
The first group of options define test semantics, controlling aspects of how doctest decides whether actual output matches an example’s expected output:

doctest.DONT_ACCEPT_TRUE_FOR_1
By default, if an expected output block contains just 1, an actual output block containing just 1 or just True is considered to be a match, and similarly for 0 versus False. When DONT_ACCEPT_TRUE_FOR_1 is specified, neither substitution is allowed. The default behavior caters to that Python changed the return type of many functions from integer to boolean; doctests expecting “little integer” output still work in these cases. This option will probably go away, but not for several years.

doctest.DONT_ACCEPT_BLANKLINE
By default, if an expected output block contains a line containing only the string <BLANKLINE>, then that line will match a blank line in the actual output. Because a genuinely blank line delimits the expected output, this is the only way to communicate that a blank line is expected. WhenDONT_ACCEPT_BLANKLINE is specified, this substitution is not allowed.

doctest.NORMALIZE_WHITESPACE
When specified, all sequences of whitespace (blanks and newlines) are treated as equal. Any sequence of whitespace within the expected output will match any sequence of whitespace within the actual output. By default, whitespace must match exactly. NORMALIZE_WHITESPACE is especially useful when a line of expected output is very long, and you want to wrap it across multiple lines in your source.

doctest.ELLIPSIS
When specified, an ellipsis marker (...) in the expected output can match any substring in the actual output. This includes substrings that span line boundaries, and empty substrings, so it’s best to keep usage of this simple. Complicated uses can lead to the same kinds of “oops, it matched too much!” surprises that .* is prone to in regular expressions.

doctest.IGNORE_EXCEPTION_DETAIL
When specified, an example that expects an exception passes if an exception of the expected type is raised, even if the exception detail does not match. For example, an example expecting ValueError: 42 will pass if the actual exception raised is ValueError: 3*14, but will fail, e.g., ifTypeError is raised.
It will also ignore the module name used in Python 3 doctest reports. Hence both of these variations will work with the flag specified, regardless of whether the test is run under Python 2.7 or Python 3.2 (or later versions):

doctest.SKIP
When specified, do not run the example at all.

The SKIP flag can also be used for temporarily “commenting out” examples.

doctest.COMPARISON_FLAGS
A bitmask or’ing together all the comparison flags above.
The second group of options controls how test failures are reported:

doctest.REPORT_UDIFF
When specified, failures that involve multi-line expected and actual outputs are displayed using a unified diff.

doctest.REPORT_CDIFF
When specified, failures that involve multi-line expected and actual outputs will be displayed using a context diff.

doctest.REPORT_NDIFF
When specified, differences are computed by difflib.Differ, using the same algorithm as the popular ndiff.py utility. This is the only method that marks differences within lines as well as across lines. For example, if a line of expected output contains digit 1 where actual output contains letterl, a line is inserted with a caret marking the mismatching column positions.

doctest.REPORT_ONLY_FIRST_FAILURE
When specified, display the first failing example in each doctest, but suppress output for all remaining examples. This will prevent doctest from reporting correct examples that break because of earlier failures; but it might also hide incorrect examples that fail independently of the first failure. When REPORT_ONLY_FIRST_FAILURE is specified, the remaining examples are still run, and still count towards the total number of failures reported; only the output is suppressed.

doctest.REPORTING_FLAGS
A bitmask or’ing together all the reporting flags above.
There is also a way to register new option flag names, though this isn’t useful unless you intend to extend doctest internals via subclassing:
doctest.register_optionflag(name)
Create a new option flag with a given name, and return the new flag’s integer value. register_optionflag() can be used when subclassingOutputChecker or DocTestRunner to create new options that are supported by your subclasses. register_optionflag() should always be called using the following idiom:
MY_FLAG = register_optionflag('MY_FLAG')

26.2.3.6. Directives

Doctest directives may be used to modify the option flags for an individual example. Doctest directives are special Python comments following an example’s source code:


26.2.3.7. Warnings
doctest is serious about requiring exact matches in expected output. If even a single character doesn’t match, the test fails. This will probably surprise you a few times, as you learn exactly what Python does and doesn’t guarantee about output. For example, when printing a dict, Python doesn’t guarantee that the key-value pairs will be printed in any particular order, so a test like

>>> foo()
{"Hermione": "hippogryph", "Harry": "broomstick"}
is vulnerable! One workaround is to do
>>>
>>> foo() == {"Hermione": "hippogryph", "Harry": "broomstick"}
True

26.2.4. Basic API

The functions testmod() and testfile() provide a simple interface to doctest that should be sufficient for most basic uses. For a less formal introduction to these two functions, see sections Simple Usage: Checking Examples in Docstrings and Simple Usage: Checking Examples in a Text File.
doctest.testfile(filename, module_relative=True, name=None, package=None, globs=None, verbose=None, report=True, optionflags=0,extraglobs=None, raise_on_error=False, parser=DocTestParser(), encoding=None)
All arguments except filename are optional, and should be specified in keyword form.
Test examples in the file named filename. Return (failure_count, test_count).
Optional argument module_relative specifies how the filename should be interpreted:
• If module_relative is True (the default), then filename specifies an OS-independent module-relative path. By default, this path is relative to the calling module’s directory; but if the package argument is specified, then it is relative to that package. To ensure OS-independence, filenameshould use / characters to separate path segments, and may not be an absolute path (i.e., it may not begin with /).
• If module_relative is False, then filename specifies an OS-specific path. The path may be absolute or relative; relative paths are resolved with respect to the current working directory.
Optional argument name gives the name of the test; by default, or if None, os.path.basename(filename) is used.
Optional argument package is a Python package or the name of a Python package whose directory should be used as the base directory for a module-relative filename. If no package is specified, then the calling module’s directory is used as the base directory for module-relative filenames. It is an error to specify package if module_relative is False.
Optional argument globs gives a dict to be used as the globals when executing examples. A new shallow copy of this dict is created for the doctest, so its examples start with a clean slate. By default, or if None, a new empty dict is used.
Optional argument extraglobs gives a dict merged into the globals used to execute examples. This works like dict.update(): if globs andextraglobs have a common key, the associated value in extraglobs appears in the combined dict. By default, or if None, no extra globals are used. This is an advanced feature that allows parameterization of doctests. For example, a doctest can be written for a base class, using a generic name for the class, then reused to test any number of subclasses by passing an extraglobs dict mapping the generic name to the subclass to be tested.
Optional argument verbose prints lots of stuff if true, and prints only failures if false; by default, or if None, it’s true if and only if '-v' is in sys.argv.
Optional argument report prints a summary at the end when true, else prints nothing at the end. In verbose mode, the summary is detailed, else the summary is very brief (in fact, empty if all tests passed).
Optional argument optionflags or’s together option flags. See section Option Flags.
Optional argument raise_on_error defaults to false. If true, an exception is raised upon the first failure or unexpected exception in an example. This allows failures to be post-mortem debugged. Default behavior is to continue running examples.
Optional argument parser specifies a DocTestParser (or subclass) that should be used to extract tests from the files. It defaults to a normal parser (i.e., DocTestParser()).
Optional argument encoding specifies an encoding that should be used to convert the file to unicode.
doctest.testmod(m=None, name=None, globs=None, verbose=None, report=True, optionflags=0, extraglobs=None, raise_on_error=False,exclude_empty=False)
All arguments are optional, and all except for m should be specified in keyword form.
Test examples in docstrings in functions and classes reachable from module m (or module __main__ if m is not supplied or is None), starting withm.__doc__.
Also test examples reachable from dict m.__test__, if it exists and is not None. m.__test__ maps names (strings) to functions, classes and strings; function and class docstrings are searched for examples; strings are searched directly, as if they were docstrings.
Only docstrings attached to objects belonging to module m are searched.
Return (failure_count, test_count).
Optional argument name gives the name of the module; by default, or if None, m.__name__ is used.
Optional argument exclude_empty defaults to false. If true, objects for which no doctests are found are excluded from consideration. The default is a backward compatibility hack, so that code still using doctest.master.summarize() in conjunction with testmod() continues to get output for objects with no tests. The exclude_empty argument to the newer DocTestFinder constructor defaults to true.
Optional arguments extraglobs, verbose, report, optionflags, raise_on_error, and globs are the same as for function testfile() above, except thatglobs defaults to m.__dict__.

26.2.5. Unittest API

As your collection of doctest’ed modules grows, you’ll want a way to run all their doctests systematically. doctest provides two functions that can be used to create unittest test suites from modules and text files containing doctests. To integrate with unittest test discovery, include a load_tests()function in your test module:
import unittest
import doctest
import my_module_with_doctests

def load_tests(loader, tests, ignore):
    tests.addTests(doctest.DocTestSuite(my_module_with_doctests))
    return tests
There are two main functions for creating unittest.TestSuite instances from text files and modules with doctests:
doctest.DocFileSuite(*paths, module_relative=True, package=None, setUp=None, tearDown=None, globs=None, optionflags=0,parser=DocTestParser(), encoding=None)
Convert doctest tests from one or more text files to a unittest.TestSuite.
The returned unittest.TestSuite is to be run by the unittest framework and runs the interactive examples in each file. If an example in any file fails, then the synthesized unit test fails, and a failureException exception is raised showing the name of the file containing the test and a (sometimes approximate) line number.
Pass one or more paths (as strings) to text files to be examined.
Options may be provided as keyword arguments:
Optional argument module_relative specifies how the filenames in paths should be interpreted:
• If module_relative is True (the default), then each filename in paths specifies an OS-independent module-relative path. By default, this path is relative to the calling module’s directory; but if the package argument is specified, then it is relative to that package. To ensure OS-independence, each filename should use / characters to separate path segments, and may not be an absolute path (i.e., it may not begin with/).
• If module_relative is False, then each filename in paths specifies an OS-specific path. The path may be absolute or relative; relative paths are resolved with respect to the current working directory.
Optional argument package is a Python package or the name of a Python package whose directory should be used as the base directory for module-relative filenames in paths. If no package is specified, then the calling module’s directory is used as the base directory for module-relative filenames. It is an error to specify package if module_relative is False.
Optional argument setUp specifies a set-up function for the test suite. This is called before running the tests in each file. The setUp function will be passed a DocTest object. The setUp function can access the test globals as the globs attribute of the test passed.
Optional argument tearDown specifies a tear-down function for the test suite. This is called after running the tests in each file. The tearDown function will be passed a DocTest object. The setUp function can access the test globals as the globs attribute of the test passed.
Optional argument globs is a dictionary containing the initial global variables for the tests. A new copy of this dictionary is created for each test. By default, globs is a new empty dictionary.
Optional argument optionflags specifies the default doctest options for the tests, created by or-ing together individual option flags. See section Option Flags. See function set_unittest_reportflags() below for a better way to set reporting options.
Optional argument parser specifies a DocTestParser (or subclass) that should be used to extract tests from the files. It defaults to a normal parser (i.e., DocTestParser()).
Optional argument encoding specifies an encoding that should be used to convert the file to unicode.
The global __file__ is added to the globals provided to doctests loaded from a text file using DocFileSuite().
doctest.DocTestSuite(module=None, globs=None, extraglobs=None, test_finder=None, setUp=None, tearDown=None, checker=None)
Convert doctest tests for a module to a unittest.TestSuite.
The returned unittest.TestSuite is to be run by the unittest framework and runs each doctest in the module. If any of the doctests fail, then the synthesized unit test fails, and a failureException exception is raised showing the name of the file containing the test and a (sometimes approximate) line number.
Optional argument module provides the module to be tested. It can be a module object or a (possibly dotted) module name. If not specified, the module calling this function is used.
Optional argument globs is a dictionary containing the initial global variables for the tests. A new copy of this dictionary is created for each test. By default, globs is a new empty dictionary.
Optional argument extraglobs specifies an extra set of global variables, which is merged into globs. By default, no extra globals are used.
Optional argument test_finder is the DocTestFinder object (or a drop-in replacement) that is used to extract doctests from the module.
Optional arguments setUp, tearDown, and optionflags are the same as for function DocFileSuite() above.
This function uses the same search technique as testmod().
Note

Unlike testmod() and DocTestFinder, this function raises a ValueError if module contains no docstrings. You can prevent this error by passing a DocTestFinder instance as the test_finder argument with its exclude_empty keyword argument set to False:
>>>
>>> finder = doctest.DocTestFinder(exclude_empty=False)
>>> suite = doctest.DocTestSuite(test_finder=finder)
Under the covers, DocTestSuite() creates a unittest.TestSuite out of doctest.DocTestCase instances, and DocTestCase is a subclass ofunittest.TestCase. DocTestCase isn’t documented here (it’s an internal detail), but studying its code can answer questions about the exact details ofunittest integration.
Similarly, DocFileSuite() creates a unittest.TestSuite out of doctest.DocFileCase instances, and DocFileCase is a subclass ofDocTestCase.
So both ways of creating a unittest.TestSuite run instances of DocTestCase. This is important for a subtle reason: when you run doctest functions yourself, you can control the doctest options in use directly, by passing option flags to doctest functions. However, if you’re writing a unittestframework, unittest ultimately controls when and how tests get run. The framework author typically wants to control doctest reporting options (perhaps, e.g., specified by command line options), but there’s no way to pass options through unittest to doctest test runners.
For this reason, doctest also supports a notion of doctest reporting flags specific to unittest support, via this function:
doctest.set_unittest_reportflags(flags)
Set the doctest reporting flags to use.
Argument flags or’s together option flags. See section Option Flags. Only “reporting flags” can be used.
This is a module-global setting, and affects all future doctests run by module unittest: the runTest() method of DocTestCase looks at the option flags specified for the test case when the DocTestCase instance was constructed. If no reporting flags were specified (which is the typical and expected case), doctest‘s unittest reporting flags are or’ed into the option flags, and the option flags so augmented are passed to theDocTestRunner instance created to run the doctest. If any reporting flags were specified when the DocTestCase instance was constructed,doctest‘s unittest reporting flags are ignored.
The value of the unittest reporting flags in effect before the function was called is returned by the function.
A collection of doctest examples that should be run in a single namespace. The constructor arguments are used to initialize the attributes of the same names.
DocTest defines the following attributes. They are initialized by the constructor, and should not be modified directly.
examples
A list of Example objects encoding the individual interactive Python examples that should be run by this test.
globs
The namespace (aka globals) that the examples should be run in. This is a dictionary mapping names to values. Any changes to the namespace made by the examples (such as binding new variables) will be reflected in globs after the test is run.
name
A string name identifying the DocTest. Typically, this is the name of the object or file that the test was extracted from.
filename
The name of the file that this DocTest was extracted from; or None if the filename is unknown, or if the DocTest was not extracted from a file.
lineno
The line number within filename where this DocTest begins, or None if the line number is unavailable. This line number is zero-based with respect to the beginning of the file.
docstring
The string that the test was extracted from, or ‘None’ if the string is unavailable, or if the test was not extracted from a string.
A single interactive example, consisting of a Python statement and its expected output. The constructor arguments are used to initialize the attributes of the same names.
Example defines the following attributes. They are initialized by the constructor, and should not be modified directly.
source
A string containing the example’s source code. This source code consists of a single Python statement, and always ends with a newline; the constructor adds a newline when necessary.
want
The expected output from running the example’s source code (either from stdout, or a traceback in case of exception). want ends with a newline unless no output is expected, in which case it’s an empty string. The constructor adds a newline when necessary.
exc_msg
The exception message generated by the example, if the example is expected to generate an exception; or None if it is not expected to generate an exception. This exception message is compared against the return value of traceback.format_exception_only(). exc_msg ends with a newline unless it’s None. The constructor adds a newline if needed.
lineno
The line number within the string containing this example where the example begins. This line number is zero-based with respect to the beginning of the containing string.
indent
The example’s indentation in the containing string, i.e., the number of space characters that precede the example’s first prompt.
options
A dictionary mapping from option flags to True or False, which is used to override default options for this example. Any option flags not contained in this dictionary are left at their default value (as specified by the DocTestRunner‘s optionflags). By default, no options are set.
A processing class used to extract the DocTests that are relevant to a given object, from its docstring and the docstrings of its contained objects.DocTests can currently be extracted from the following object types: modules, functions, classes, methods, staticmethods, classmethods, and properties.
The optional argument verbose can be used to display the objects searched by the finder. It defaults to False (no output).
The optional argument parser specifies the DocTestParser object (or a drop-in replacement) that is used to extract doctests from docstrings.
If the optional argument recurse is false, then DocTestFinder.find() will only examine the given object, and not any contained objects.
If the optional argument exclude_empty is false, then DocTestFinder.find() will include tests for objects with empty docstrings.

DocTestFinder defines the following method:

find(obj[, name][, module][, globs][, extraglobs])
Return a list of the DocTests that are defined by obj‘s docstring, or by any of its contained objects’ docstrings.
The optional argument name specifies the object’s name; this name will be used to construct names for the returned DocTests. If name is not specified, then obj.__name__ is used.
The optional parameter module is the module that contains the given object. If the module is not specified or is None, then the test finder will attempt to automatically determine the correct module. The object’s module is used:
• As a default namespace, if globs is not specified.
• To prevent the DocTestFinder from extracting DocTests from objects that are imported from other modules. (Contained objects with modules other than module are ignored.)
• To find the name of the file containing the object.
• To help find the line number of the object within its file.
If module is False, no attempt to find the module will be made. This is obscure, of use mostly in testing doctest itself: if module is False, or isNone but cannot be found automatically, then all objects are considered to belong to the (non-existent) module, so all contained objects will (recursively) be searched for doctests.
The globals for each DocTest is formed by combining globs and extraglobs (bindings in extraglobs override bindings in globs). A new shallow copy of the globals dictionary is created for each DocTest. If globs is not specified, then it defaults to the module’s __dict__, if specified, or {}otherwise. If extraglobs is not specified, then it defaults to {}.
A processing class used to extract interactive examples from a string, and use them to create a DocTest object.

DocTestParser defines the following methods:

get_doctest(string, globs, name, filename, lineno)
Extract all doctest examples from the given string, and collect them into a DocTest object.
globs, name, filename, and lineno are attributes for the new DocTest object. See the documentation for DocTest for more information.
get_examples(string, name='<string>')
Extract all doctest examples from the given string, and return them as a list of Example objects. Line numbers are 0-based. The optional argumentname is a name identifying this string, and is only used for error messages.
parse(string, name='<string>')
Divide the given string into examples and intervening text, and return them as a list of alternating Examples and strings. Line numbers for theExamples are 0-based. The optional argument name is a name identifying this string, and is only used for error messages.
A processing class used to execute and verify the interactive examples in a DocTest.
The comparison between expected outputs and actual outputs is done by an OutputChecker. This comparison may be customized with a number of option flags; see section Option Flags for more information. If the option flags are insufficient, then the comparison may also be customized by passing a subclass of OutputChecker to the constructor.
The test runner’s display output can be controlled in two ways. First, an output function can be passed to TestRunner.run(); this function will be called with strings that should be displayed. It defaults to sys.stdout.write. If capturing the output is not sufficient, then the display output can be also customized by subclassing DocTestRunner, and overriding the methods report_start(), report_success(),report_unexpected_exception(), and report_failure().
The optional keyword argument checker specifies the OutputChecker object (or drop-in replacement) that should be used to compare the expected outputs to the actual outputs of doctest examples.
The optional keyword argument verbose controls the DocTestRunner‘s verbosity. If verbose is True, then information is printed about each example, as it is run. If verbose is False, then only failures are printed. If verbose is unspecified, or None, then verbose output is used iff the command-line switch -v is used.
The optional keyword argument optionflags can be used to control how the test runner compares expected output to actual output, and how it displays failures. For more information, see section Option Flags.

DocTestParser defines the following methods:

report_start(out, test, example)
Report that the test runner is about to process the given example. This method is provided to allow subclasses of DocTestRunner to customize their output; it should not be called directly.
example is the example about to be processed. test is the test containing example. out is the output function that was passed toDocTestRunner.run().
report_success(out, test, example, got)
Report that the given example ran successfully. This method is provided to allow subclasses of DocTestRunner to customize their output; it should not be called directly.
example is the example about to be processed. got is the actual output from the example. test is the test containing example. out is the output function that was passed to DocTestRunner.run().
report_failure(out, test, example, got)
Report that the given example failed. This method is provided to allow subclasses of DocTestRunner to customize their output; it should not be called directly.
example is the example about to be processed. got is the actual output from the example. test is the test containing example. out is the output function that was passed to DocTestRunner.run().
report_unexpected_exception(out, test, example, exc_info)
Report that the given example raised an unexpected exception. This method is provided to allow subclasses of DocTestRunner to customize their output; it should not be called directly.
example is the example about to be processed. exc_info is a tuple containing information about the unexpected exception (as returned bysys.exc_info()). test is the test containing example. out is the output function that was passed to DocTestRunner.run().
run(test, compileflags=None, out=None, clear_globs=True)
Run the examples in test (a DocTest object), and display the results using the writer function out.
The examples are run in the namespace test.globs. If clear_globs is true (the default), then this namespace will be cleared after the test runs, to help with garbage collection. If you would like to examine the namespace after the test completes, then use clear_globs=False.
compileflags gives the set of flags that should be used by the Python compiler when running the examples. If not specified, then it will default to the set of future-import flags that apply to globs.
The output of each example is checked using the DocTestRunner‘s output checker, and the results are formatted by theDocTestRunner.report_*() methods.
summarize(verbose=None)
Print a summary of all the test cases that have been run by this DocTestRunner, and return a named tuple TestResults(failed, attempted).
The optional verbose argument controls how detailed the summary is. If the verbosity is not specified, then the DocTestRunner‘s verbosity is used.
ass doctest.OutputChecker
A class used to check the whether the actual output from a doctest example matches the expected output. OutputChecker defines two methods:check_output(), which compares a given pair of outputs, and returns true if they match; and output_difference(), which returns a string describing the differences between two outputs.
OutputChecker defines the following methods:
check_output(want, got, optionflags)
Return True iff the actual output from an example (got) matches the expected output (want). These strings are always considered to match if they are identical; but depending on what option flags the test runner is using, several non-exact match types are also possible. See section Option Flags for more information about option flags.
output_difference(example, got, optionflags)
Return a string describing the differences between the expected output for a given example (example) and the actual output (got). optionflags is the set of option flags used to compare want and got.
)

Convert text with examples to a script.

Argument s is a string containing doctest examples. The string is converted to a Python script, where doctest examples in s are converted to regular code, and everything else is converted to Python comments. The generated script is returned as a string. For example,
import doctest
print(doctest.script_from_examples(r"""
    Set x and y to 1 and 2.
    >>> x, y = 1, 2

    Print their sum:
    >>> print(x+y)
    3
"""))
displays:
# Set x and y to 1 and 2.
x, y = 1, 2
#
# Print their sum:
print(x+y)
# Expected:
## 3
This function is used internally by other functions (see below), but can also be useful when you want to transform an interactive Python session into a Python script.
test.testsource(module, name)
Convert the doctest for an object to a script.
Argument module is a module object, or dotted name of a module, containing the object whose doctests are of interest. Argument name is the name (within the module) of the object with the doctests of interest. The result is a string, containing the object’s docstring converted to a Python script, as described for script_from_examples() above. For example, if module a.py contains a top-level function f(), then
import a, doctest
print(doctest.testsource(a, "a.f"))
prints a script version of function f()‘s docstring, with doctests converted to code, and the rest placed in comments.
doctest.debug(module, name, pm=False)

Debug the doctests for an object.

The module and name arguments are the same as for function testsource() above. The synthesized Python script for the named object’s docstring is written to a temporary file, and then that file is run under the control of the Python debugger, pdb.
A shallow copy of module.__dict__ is used for both local and global execution context.
Optional argument pm controls whether post-mortem debugging is used. If pm has a true value, the script file is run directly, and the debugger gets involved only if the script terminates via raising an unhandled exception. If it does, then post-mortem debugging is invoked, via pdb.post_mortem(), passing the traceback object from the unhandled exception. If pm is not specified, or is false, the script is run under the debugger from the start, via passing an appropriate exec() call to pdb.run().
doctest.debug_src(src, pm=False, globs=None)

Debug the doctests in a string.

This is like function debug() above, except that a string containing doctest examples is specified directly, via the src argument.
Optional argument pm has the same meaning as in function debug() above.
Optional argument globs gives a dictionary to use as both local and global execution context. If not specified, or None, an empty dictionary is used. If specified, a shallow copy of the dictionary is used.
The DebugRunner class, and the special exceptions it may raise, are of most interest to testing framework authors, and will only be sketched here. See the source code, and especially DebugRunner‘s docstring (which is a doctest!) for more details:
class doctest.DebugRunner(checker=None, verbose=None, optionflags=0)
A subclass of DocTestRunner that raises an exception as soon as a failure is encountered. If an unexpected exception occurs, anUnexpectedException exception is raised, containing the test, the example, and the original exception. If the output doesn’t match, then aDocTestFailure exception is raised, containing the test, the example, and the actual output.
For information about the constructor parameters and methods, see the documentation for DocTestRunner in section Advanced API.
There are two exceptions that may be raised by DebugRunner instances:
exception doctest.DocTestFailure(test, example, got)
An exception raised by DocTestRunner to signal that a doctest example’s actual output did not match its expected output. The constructor arguments are used to initialize the attributes of the same names.

DocTestFailure defines the following attributes:

DocTestFailure.test
The DocTest object that was being run when the example failed.
DocTestFailure.example
The Example that failed.
DocTestFailure.got
The example’s actual output.
exception doctest.UnexpectedException(test, example, exc_info)
An exception raised by DocTestRunner to signal that a doctest example raised an unexpected exception. The constructor arguments are used to initialize the attributes of the same names.

UnexpectedException defines the following attributes:

UnexpectedException.test
The DocTest object that was being run when the example failed.
UnexpectedException.example
The Example that failed.
UnexpectedException.exc_info