Mastering Python Second Edition Release Code

2022-05-05 18:25:55 +02:00
commit 3223a43fe3
454 changed files with 20230 additions and 0 deletions
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+Chapter 11, Debugging
+##############################################################################
+
+| Solving bugs demonstrates several methods of hunting down bugs using tracing, logging and interactive debugging.
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+import os
+import inspect
+import linecache
+
+
+def print_code():
+    while True:
+        info = inspect.stack()[1]
+        lineno = info.lineno
+        function = info.function
+        # Strip the path from the filename
+        filename = os.path.split(info.filename)[-1]
+        # Fetch the next line of code
+        code = linecache.getline(info.filename, lineno + 1)
+        print(f'{filename}:{lineno}:{function}: {code.strip()}')
+        yield
+
+
+# Always prime the generator
+print_code = print_code()
+
+
+def some_test_function(a, b):
+    next(print_code)
+    c = a + b
+    next(print_code)
+    return c
+
+
+some_test_function('a', 'b')
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+>>> def hiding_generator():
+...     print('a')
+...     yield 'first value'
+...     print('b')
+...     yield 'second value'
+...     print('c')
+
+>>> generator = hiding_generator()
+
+>>> next(generator)
+a
+'first value'
+
+>>> next(generator)
+b
+'second value'
+
+>>> next(generator)
+Traceback (most recent call last):
+...
+StopIteration
+
+##############################################################################
+
+>>> import os
+>>> import inspect
+>>> import linecache
+
+
+>>> def print_code():
+...     while True:
+...         info = inspect.stack()[1]
+...         lineno = info.lineno + 1
+...         function = info.function
+...         # Fetch the next line of code
+...         code = linecache.getline(info.filename, lineno)
+...         print(f'{lineno:03d} {function}: {code.strip()}')
+...         yield
+
+
+# Always prime the generator
+
+>>> print_code = print_code()
+
+
+>>> def some_test_function(a, b):
+...     next(print_code)
+...     c = a + b
+...     next(print_code)
+...     return c
+
+>>> some_test_function('a', 'b')
+003 some_test_function: c = a + b
+005 some_test_function: return c
+'ab'
+
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+def some_test_function(a, b):
+    c = a + b
+    return c
+
+
+print(some_test_function('a', 'b'))
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+ --- modulename: T_02_selective_trace, funcname: some_test_function
+0.00 T_02_selective_trace.py(19):     c = a + b
+0.00 T_02_selective_trace.py(20):     return c
+ab
+ --- modulename: contextlib, funcname: __exit__
+0.00 contextlib.py(...):         if typ... is None:
+0.00 contextlib.py(...):             try:
+0.00 contextlib.py(...):                 next(self.gen)
+ --- modulename: T_02_selective_trace, funcname: trace
+0.00 T_02_selective_trace.py(12):     sys.settrace(None)
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+import sys
+import trace as trace_module
+import contextlib
+
+
+@contextlib.contextmanager
+def trace(count=False, trace=True, timing=True):
+    tracer = trace_module.Trace(
+        count=count, trace=trace, timing=timing)
+    sys.settrace(tracer.globaltrace)
+    yield tracer
+    sys.settrace(None)
+
+    result = tracer.results()
+    result.write_results(show_missing=False, summary=True)
+
+
+def some_test_function(a, b):
+    c = a + b
+    return c
+
+
+with trace():
+    print(some_test_function('a', 'b'))
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+ --- modulename: T_03_filename_trace, funcname: some_test_function
+T_03_filename_trace.py(27):     c = a + b
+T_03_filename_trace.py(28):     return c
+ab
+ --- modulename: T_03_filename_trace, funcname: trace
+T_03_filename_trace.py(20):     sys.settrace(None)
+lines   cov%   module   (path)
+    3   100%   T_03_filename_trace   (/CH_11_debugging/T_03_filename_trace.py)
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+import sys
+import trace as trace_module
+import contextlib
+
+
+@contextlib.contextmanager
+def trace(filename):
+    tracer = trace_module.Trace()
+
+    def custom_trace(frame, event, arg):
+        # Only trace for the given filename
+        if filename != frame.f_code.co_filename:
+            return custom_trace
+
+        # Let globaltrace handle the rest
+        return tracer.globaltrace(frame, event, arg)
+
+    sys.settrace(custom_trace)
+    yield tracer
+    sys.settrace(None)
+
+    result = tracer.results()
+    result.write_results(show_missing=False, summary=True)
+
+
+def some_test_function(a, b):
+    c = a + b
+    return c
+
+
+# Pass our current filename as `__file__`
+with trace(filename=__file__):
+    print(some_test_function('a', 'b'))
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+DEBUG:root:add(a=1, b=123): 124
+DEBUG:root:add(a=1, b=456): 457
+DEBUG:root:add(a=456, b=1): 457
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+import pprint
+import inspect
+import logging
+import functools
+
+
+def debug(function):
+    @functools.wraps(function)
+    def _debug(*args, **kwargs):
+        # Make sure `result` is always defined
+        result = None
+        try:
+            result = function(*args, **kwargs)
+            return result
+        finally:
+            # Extract the signature from the function
+            signature = inspect.signature(function)
+            # Fill the arguments
+            arguments = signature.bind(*args, **kwargs)
+            # NOTE: This only works for Python 3.5 and up!
+            arguments.apply_defaults()
+
+            logging.debug('%s(%s): %s' % (
+                function.__qualname__,
+                ', '.join('%s=%r' % (k, v) for k, v in
+                          arguments.arguments.items()),
+                pprint.pformat(result),
+            ))
+
+    return _debug
+
+
+@debug
+def add(a, b=123):
+    return a + b
+
+
+if __name__ == '__main__':
+    logging.basicConfig(level=logging.DEBUG)
+
+    add(1)
+    add(1, 456)
+    add(b=1, a=456)
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+[DEBUG] T_05_logging_config.py:20:_debug: add(a=1, b=123): 124
+[DEBUG] T_05_logging_config.py:20:_debug: add(a=1, b=456): 457
+[DEBUG] T_05_logging_config.py:20:_debug: add(a=456, b=1): 457
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+import pprint
+import inspect
+import logging
+import functools
+
+
+def debug(function):
+    @functools.wraps(function)
+    def _debug(*args, **kwargs):
+        try:
+            result = function(*args, **kwargs)
+        finally:
+            # Extract the signature from the function
+            signature = inspect.signature(function)
+            # Fill the arguments
+            arguments = signature.bind(*args, **kwargs)
+            # NOTE: This only works for Python 3.5 and up!
+            arguments.apply_defaults()
+
+            logging.debug('%s(%s): %s' % (
+                function.__qualname__,
+                ', '.join('%s=%r' % (k, v) for k, v in
+                          arguments.arguments.items()),
+                pprint.pformat(result),
+            ))
+
+    return _debug
+
+
+@debug
+def add(a, b=123):
+    return a + b
+
+
+if __name__ == '__main__':
+    log_format = (
+        # Removed %(relativeCreated)d because of test unstability
+        '[%(levelname)s] '
+        '%(filename)s:%(lineno)d:%(funcName)s: %(message)s'
+    )
+    logging.basicConfig(level=logging.DEBUG, format=log_format)
+
+    add(1)
+    add(1, 456)
+    add(b=1, a=456)
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+import traceback
+
+
+class ShowMyStack:
+
+    def run(self, limit=None):
+        print('Before stack print')
+        traceback.print_stack(limit=limit)
+        print('After stack print')
+
+
+class InheritShowMyStack(ShowMyStack):
+    pass
+
+
+if __name__ == '__main__':
+    show_stack = InheritShowMyStack()
+
+    print('Stack without limit')
+    show_stack.run()
+    print()
+
+    print('Stack with limit 1')
+    show_stack.run(1)
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+import ctypes
+
+# Get memory address 0, your kernel shouldn't allow this:
+ctypes.string_at(0)
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+import ctypes
+
+try:
+    # Get memory address 0, your kernel shouldn't allow this:
+    ctypes.string_at(0)
+except Exception as e:
+    print('Got exception:', e)
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+import ctypes
+import faulthandler
+
+faulthandler.enable()
+
+# Get memory address 0, your kernel shouldn't allow this:
+ctypes.string_at(0)
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+import code
+
+
+def start_console():
+    some_variable = 123
+    print(f'Launching console, some_variable: {some_variable}')
+    code.interact(banner='console:', local=locals())
+    print(f'Exited console, some_variable: {some_variable}')
+
+
+if __name__ == '__main__':
+    start_console()
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+import pdb
+
+
+def go_to_debugger():
+    some_variable = 123
+    print('Starting pdb trace')
+    pdb.set_trace()
+    print(f'Finished pdb, some_variable: {some_variable}')
+
+
+if __name__ == '__main__':
+    go_to_debugger()
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+import pdb
+
+
+def print_value(value):
+    print('value:', value)
+
+
+if __name__ == '__main__':
+    pdb.set_trace()
+    for i in range(5):
+        print_value(i)
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+print('This still works')
+1 / 0
+print('We will never reach this')
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+def do_nothing(i):
+    pass
+
+
+for i in range(10):
+    do_nothing(i)
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+def print_value(value):
+    print('value:', value)
+
+
+if __name__ == '__main__':
+    for i in range(5):
+        print_value(i)