Learn Python using Jupyter Notebook

With Jupyter, PyHamcrest, and a little test code tying them together, you can teach any Python content that applies to unit testing.

##Python video tutorial column will give you a detailed introduction~

Some things about the Ruby community have always impressed me, two examples of which are the commitment to testing and the emphasis on ease of getting started. The best example of both is Ruby Koans, where you can learn Ruby by fixing tests.

If we could bring these amazing tools to Python, we should be able to do better. Yes, using Jupyter Notebook, PyHamcrest, and a little duct tape-like glue code, we can make a tutorial that includes instruction, working code, and code that needs fixing.

First, you need some "tape". Typically, you'll use some nifty command-line tester like pytest or virtue to do your testing. Often, you won't even run it directly. You use a tool like tox or nox to run it. However, with Jupyter, you need to write a small piece of glue code where you can run the test directly.

Luckily, this code is short and simple:

import unittest

def run_test(klass):
    suite = unittest.TestLoader().loadTestsFromTestCase(klass)
    unittest.TextTestRunner(verbosity=2).run(suite)
    return klass复制代码

Now, the gear is ready for your first practice session.

When teaching, it's always a good idea to start with a simple exercise to build confidence.

So, let's fix a very simple test:

@run_test
class TestNumbers(unittest.TestCase):
   
    def test_equality(self):
        expected_value = 3 # 只改这一行
        self.assertEqual(1+1, expected_value)复制代码

    test_equality (__main__.TestNumbers) ... FAIL
   
    ======================================================================
    FAIL: test_equality (__main__.TestNumbers)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-7-5ebe25bc00f3>", line 6, in test_equality
        self.assertEqual(1+1, expected_value)
    AssertionError: 2 != 3
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.002s
   
    FAILED (failures=1)复制代码

"Change just this line" is a useful tag for students. It indicates exactly what needs to be modified. Otherwise, students can fix the test by changing the first line to

return.

In this case, the fix is ​​easy:

@run_test
class TestNumbers(unittest.TestCase):
   
    def test_equality(self):
        expected_value = 2 # 修复后的代码行
        self.assertEqual(1+1, expected_value)复制代码

    test_equality (__main__.TestNumbers) ... ok
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.002s
   
    OK复制代码

Soon, however, the

unittest library's native assertions will prove insufficient. In pytest this problem is solved by rewriting the bytecode in assert to have magic properties and various heuristics. But this is not easy to achieve in Jupyter notebook. It’s time to dig out a good assertion library: PyHamcrest.

from hamcrest import *
@run_test
class TestList(unittest.TestCase):
   
    def test_equality(self):
        things = [1,
                  5, # 只改这一行
                  3]
        assert_that(things, has_items(1, 2, 3))复制代码

    test_equality (__main__.TestList) ... FAIL
   
    ======================================================================
    FAIL: test_equality (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-11-96c91225ee7d>", line 8, in test_equality
        assert_that(things, has_items(1, 2, 3))
    AssertionError:
    Expected: (a sequence containing <1> and a sequence containing <2> and a sequence containing <3>)
         but: a sequence containing <2> was <[1, 5, 3]>
   
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.004s
   
    FAILED (failures=1)复制代码

PyHamcrest isn't just good at flexible assertions, it's also good at clear error messages. Because of this, the problem is obvious.

[1, 5, 3] does not contain 2, and looks ugly:

@run_test
class TestList(unittest.TestCase):
   
    def test_equality(self):
        things = [1,
                  2, # 改完的行
                  3]
        assert_that(things, has_items(1, 2, 3))复制代码

    test_equality (__main__.TestList) ... ok
   
    ----------------------------------------------------------------------
    Ran 1 test in 0.001s
   
    OK复制代码

Using Jupyter, PyHamcrest and a little test glue code, you can Teach any Python topic applicable to unit testing.

For example, the following helps show the differences between Python's different ways of stripping whitespace from strings.

source_string = "  hello world  "

@run_test
class TestList(unittest.TestCase):
   
    # 这是个赠品：它可以工作！
    def test_complete_strip(self):
        result = source_string.strip()
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world")))

    def test_start_strip(self):
        result = source_string # 只改这一行
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world  ")))

    def test_end_strip(self):
        result = source_string # 只改这一行
        assert_that(result,
                   all_of(starts_with("  hello"), ends_with("world")))复制代码

    test_complete_strip (__main__.TestList) ... ok
    test_end_strip (__main__.TestList) ... FAIL
    test_start_strip (__main__.TestList) ... FAIL
   
    ======================================================================
    FAIL: test_end_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-16-3db7465bd5bf>", line 19, in test_end_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with &#39;  hello&#39; and a string ending with &#39;world&#39;)
         but: a string ending with &#39;world&#39; was &#39;  hello world  &#39;
   
   
    ======================================================================
    FAIL: test_start_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-16-3db7465bd5bf>", line 14, in test_start_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with &#39;hello&#39; and a string ending with &#39;world  &#39;)
         but: a string starting with &#39;hello&#39; was &#39;  hello world  &#39;
   
   
    ----------------------------------------------------------------------
    Ran 3 tests in 0.006s
   
    FAILED (failures=2)复制代码

Ideally, students will realize that

.lstrip() and .rstrip() will meet their needs. But if they don't do that and instead try to use .strip() everywhere:

source_string = "  hello world  "

@run_test
class TestList(unittest.TestCase):
   
    # 这是个赠品：它可以工作！
    def test_complete_strip(self):
        result = source_string.strip()
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world")))

    def test_start_strip(self):
        result = source_string.strip() # 改完的行
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world  ")))

    def test_end_strip(self):
        result = source_string.strip() # 改完的行
        assert_that(result,
                   all_of(starts_with("  hello"), ends_with("world")))复制代码

    test_complete_strip (__main__.TestList) ... ok
    test_end_strip (__main__.TestList) ... FAIL
    test_start_strip (__main__.TestList) ... FAIL
   
    ======================================================================
    FAIL: test_end_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-17-6f9cfa1a997f>", line 19, in test_end_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with &#39;  hello&#39; and a string ending with &#39;world&#39;)
         but: a string starting with &#39;  hello&#39; was &#39;hello world&#39;
   
   
    ======================================================================
    FAIL: test_start_strip (__main__.TestList)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "<ipython-input-17-6f9cfa1a997f>", line 14, in test_start_strip
        assert_that(result,
    AssertionError:
    Expected: (a string starting with &#39;hello&#39; and a string ending with &#39;world  &#39;)
         but: a string ending with &#39;world  &#39; was &#39;hello world&#39;
   
   
    ----------------------------------------------------------------------
    Ran 3 tests in 0.007s
   
    FAILED (failures=2)复制代码

they'll get a different error message showing that too much whitespace has been removed:

source_string = "  hello world  "

@run_test
class TestList(unittest.TestCase):
   
    # 这是个赠品：它可以工作！
    def test_complete_strip(self):
        result = source_string.strip()
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world")))

    def test_start_strip(self):
        result = source_string.lstrip() # Fixed this line
        assert_that(result,
                   all_of(starts_with("hello"), ends_with("world  ")))

    def test_end_strip(self):
        result = source_string.rstrip() # Fixed this line
        assert_that(result,
                   all_of(starts_with("  hello"), ends_with("world")))复制代码

    test_complete_strip (__main__.TestList) ... ok
    test_end_strip (__main__.TestList) ... ok
    test_start_strip (__main__.TestList) ... ok
   
    ----------------------------------------------------------------------
    Ran 3 tests in 0.005s
   
    OK复制代码

In a more realistic tutorial, there will be more examples and more explanations. This technique of using Jupyter Notebook can be used for some examples, and some examples need to be corrected. It can be used for real-time teaching, for video lessons, and even for more other scattered purposes, allowing students to complete a tutorial by themselves.

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