Kurage Notes

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Tips for debugging (Lab1) ​

https://inst.eecs.berkeley.edu/~cs61a/fa23/lab/lab01/

https://inst.eecs.berkeley.edu/~cs61a/fa23/articles/debugging/

https://www.composingprograms.com/pages/15-control.html

Traceback Messages ​

File "<file name>", line <number>, in <function>

The traceback is organized with the "most recent call last."

Error Messages ​

<error type>: <error message>

Doctest ​

Trivia about Functions (L2 & L3)

  1. Write some tests before you write code
  2. Write more tests after you write code
  3. Test edge cases

Interactively Running Doctests ​

Also can be used in python interactive mode.

bash
$ python3 -i test.py
python
>>> from doctest import testmod
>>> testmod()
TestResults(failed=0, attempted=12)
>>> from doctest import run_docstring_examples
>>> run_docstring_examples(sum_naturals, globals(), True) # (function_name, globals() returns the global env, whether to verbose output)
Finding tests in NoName
Trying:
    sum_naturals(10)
Expecting:
    55
ok
Trying:
    sum_naturals(100)
Expecting:
    5050
ok

A test that applies a single function is called a unit test.

Debug print ​

Normal case ​

Just add this if you want to check a certain value at a certain point of execution.

python
print('DEBUG: foo was this:', foo)

While loops ​

In While loops: debug print shows the times it has looped

python
i = 0
while i < n:
    i += func(i)
    print('DEBUG: i is', i)

assert statements ​

Python has a feature known as an assert statement, which lets you test that a condition is true, and print an error message otherwise in a single line.

python
>>> assert 4 > 3, 'This will never be displayed'
>>> assert 2 > 3, 'There\'s an error'
...
AssertionError: There's an error

This is useful if you know that certain conditions need to be true at certain points in your program.

python
def double(x):
    assert isinstance(x, int), "The input to double(x) must be an integer"
    return 2 * x

Crashes are better than running errors! Having asserts in your code makes it far more likely that your code will crash if it has a bug in it.

Also test the extreme conditions.

python
"""fib_test.py
After the fib.py file.
"""
def fib_test():
	assert fib(2) == 1, 'The 2nd Fibonacci number should be 1'
	assert fib(3) == 1, 'The 3rd Fibonacci number should be 1'
	assert fib(50) == 7778742049, 'Error at the 50th Fibonacci number'