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Completed the aobut_string_manipulation koan #7

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34 changes: 17 additions & 17 deletions python2/koans/about_string_manipulation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10,38 +10,38 @@ def test_use_format_to_interpolate_variables(self):
value1 = 'one'
value2 = 2
string = "The values are {0} and {1}".format(value1, value2)
self.assertEqual(__, string)
self.assertEqual("The values are one and 2", string)

def test_formatted_values_can_be_shown_in_any_order_or_be_repeated(self):
value1 = 'doh'
value2 = 'DOH'
string = "The values are {1}, {0}, {0} and {1}!".format(value1, value2)
self.assertEqual(__, string)
self.assertEqual("The values are DOH, doh, doh and DOH!", string)

def test_any_python_expression_may_be_interpolated(self):
import math # import a standard python module with math functions

decimal_places = 4
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

See this and this.

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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@glpuga glpuga Dec 11, 2019 •
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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?


def test_you_can_get_a_substring_from_a_string(self):
string = "Bacon, lettuce and tomato"
self.assertEqual(__, string[7:10])
self.assertEqual("let", string[7:10])

def test_you_can_get_a_single_character_from_a_string(self):
string = "Bacon, lettuce and tomato"
self.assertEqual(__, string[1])
self.assertEqual("a", string[1])

def test_single_characters_can_be_represented_by_integers(self):
self.assertEqual(__, ord('a'))
self.assertEqual(__, ord('b') == (ord('a') + 1))
self.assertEqual(97, ord('a'))
self.assertEqual(True, ord('b') == (ord('a') + 1))

def test_strings_can_be_split(self):
string = "Sausage Egg Cheese"
words = string.split()
self.assertEqual([__, __, __], words)
self.assertEqual(["Sausage", "Egg", "Cheese"], words)

def test_strings_can_be_split_with_different_patterns(self):
import re # import python regular expression library
Expand All @@ -51,26 +51,26 @@ def test_strings_can_be_split_with_different_patterns(self):

words = pattern.split(string)

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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@stevendes stevendes Dec 11, 2019 •
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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


# `pattern` is a Python regular expression pattern which matches
# ',' or ';'

def test_raw_strings_do_not_interpret_escape_characters(self):
string = r'\n'
self.assertNotEqual('\n', string)
self.assertEqual(__, string)
self.assertEqual(__, len(string))
self.assertEqual("\\n", string)
self.assertEqual(2, len(string))

# Useful in regular expressions, file paths, URLs, etc.

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.


def test_strings_can_change_case(self):
self.assertEqual(__, 'guido'.capitalize())
self.assertEqual(__, 'guido'.upper())
self.assertEqual(__, 'TimBot'.lower())
self.assertEqual(__, 'guido van rossum'.title())
self.assertEqual(__, 'ToTaLlY aWeSoMe'.swapcase())
self.assertEqual("Guido", 'guido'.capitalize())
self.assertEqual("GUIDO", 'guido'.upper())
self.assertEqual("timbot", 'TimBot'.lower())
self.assertEqual("Guido Van Rossum", 'guido van rossum'.title())
self.assertEqual("tOtAlLy AwEsOmE", 'ToTaLlY aWeSoMe'.swapcase())