Completed the aobut_string_manipulation koan #7
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| words = pattern.split(string) | ||
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| self.assertEqual([__, __, __, __], words) | ||
| self.assertEqual(["the", "rain", "in", "spain"], words) |
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50 pattern = re.compile(',|;')
I'm also not sure how this works
This is an example of a Regular Expression (regexp, for short). Notice that the re module is imported first. See this for an introduction. You'll see more of this later, don't worry.
In short, split splits the string into sub-strings separated by instances of pattern, whereas the pattern ,|; matches whenever you find a , OR a ;.
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Q: Say I have a string with a human readable list of ingredients: "flour, tomato souse, 2 eggs, cheese, ham, and olives". Find a regex pattern that will split that string into a list of ingredients for a machine, such as [ "flour", "tomato souse", "2 eggs", "cheese", "ham", "olives"]
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Could that be pattern=re.compile(,) ?
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Nop, there are spaces and and 'and" too! You'll need a pattern that matches those too.
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I think my best option is pattern=re.compile(,|and), because including the space separates the 2 and the eggs
| def test_strings_can_be_joined(self): | ||
| words = ["Now", "is", "the", "time"] | ||
| self.assertEqual(__, ' '.join(words)) | ||
| self.assertEqual("Now is the time", ' '.join(words)) |
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Notice the difference between " ".join(words) and "".join(words).
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The string at the start is the separator, right?
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That's right. If you execute 'SEP'.join(words) you'll get 'NowSEPisSEPtheSEPtime'.
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Same with any other string.
| string = "The square root of 5 is {0:.{1}f}".format(math.sqrt(5), \ | ||
| decimal_places) | ||
| self.assertEqual(__, string) | ||
| self.assertEqual("The square root of 5 is 2.2361", string) |
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27 string = "The square root of 5 is {0:.{1}f}".format(math.sqrt(5), \decimal_places)
I'm not sure about what the {0:.{1}f exactly does
In short {0:.{1}f} is saying: get the argument {0}, but add formatting to it, interpreting as a floating point value (the f) and such that the precision (number of digits after the decimal point) is whatever the value of the {1} argument says (in this case, 4).
I hope that helps. Play with it a little, it's very similar to C-language string formatting.
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Given:
days = dict()
days["Mercury"] = 87.96
days["Venus"] = 224.68
days["Earth"] = 365.26
days["Mars"] = 686.98
Printing this with:
for key,value in days.items():
print("{0} {1}".format(key, value))
Looks ugly for a user interface (try). Give me a code snippet that prints this in tidy columns, using 10 characters for the planet name field width, and 20 for the period revolution days, with 3 for the precision. It should look like this:
Mercury 87.960
Earth 365.260
Venus 224.680
Mars 686.980
PS: Notice the rows are not in the same order as I added them to the dict...why?
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I think is ordering by the key with a higher value, but I'm not sure.
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I think is ordering by the key with a higher value, but I'm not sure.
Think again https://github.com/stevendes/python_koans/pull/6/files#diff-7ff6c7eb24ff198b3e2fab6c93748dd2R36
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What about the code I asked above?
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So it's because the dictionary doesn't really have an order?
Completed and ready for review!
I also have some questions in the following regards:
27 string = "The square root of 5 is {0:.{1}f}".format(math.sqrt(5), \decimal_places)I'm not sure about what the
{0:.{1}fexactly does50 pattern = re.compile(',|;')I'm also not sure how this works