Python for Programmers: More String Methods

• We've seen a few string methods already. This lesson will cover some more common string methods.

• .upper converts the entire string to uppercase.

• >

  "Amir".upper()

  Result:

  'AMIR'

• .lower converts it to lowercase.

• >

  "Amir".lower()

  Result:

  'amir'

• The .split method splits a string by a given separator. It gives us a list of the strings that occur between the separators.

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  "a,b,c".split(",")

  Result:

  Run Code

• >

  "a:b".split(":")

  Result:

  ['a', 'b']

• If the string doesn't contain the separator, .split returns a list with the original string.

• >

  "a,b,c".split("%")

  Result:

  ['a,b,c']

• The separator can be multiple characters. Python only breaks the string in places where the entire separator appears together.

• >

  "a, b, c".split(", ")

  Result:

  ['a', 'b', 'c']

• It's easy to make mistakes in the separator string. For example, our string might be "a, b, c". If we split on just ",", then our list will include the spaces in its strings.

• >

  "a, b, c".split(",")

  Result:

  Run Code

• If the string starts with the separator, we get an empty string "" as the first element.

• >

  "$17$18".split("$")

  Result:

  Run Code

• If the string ends with the separator, we get an empty string as the last element.

• >

  "17.18.".split(".")

  Result:

  ['17', '18', '']

• >

  ":abc:".split(":")

  Result:

  ['', 'abc', '']

• .splitlines splits multi-line text into a list of lines, but we don't need to provide a separator. It handles newlines (\n), carriage returns (\r), and Windows-style line terminators (\r\n). This makes .splitlines work across different operating systems. Getting the same effect with .split would take a lot more work.

• >

  "Amir\nBetty\r\nCindy".splitlines()

  Result:

  ['Amir', 'Betty', 'Cindy']

• .join is the opposite of .split. It combines list elements into one string, inserting the provided string between the elements.

• >

  cat_names = ["Keanu", "Ms. Fluff", "Wilford"]
  ", ".join(cat_names)

  Result:

  Run Code

• >

  animal_names = ["cat", "dog", "owl"]
  ", ".join(animal_names)

  Result:

  'cat, dog, owl'

• If we combine .join and .split, we get the list that we started with.

• >

  cat_names = ["Keanu", "Ms. Fluff", "Wilford"]
  ", ".join(cat_names).split(", ")

  Result:

  ['Keanu', 'Ms. Fluff', 'Wilford']

• .strip removes leading and trailing whitespace. That includes spaces, newlines (\n), line feeds (\r), tabs (\t), and some other less-common whitespace characters.

• >

  "    Hello, Amir\n".strip()

  Result:

  'Hello, Amir'

• Without an argument, .strip removes whitespace, as shown above. But we can also provide a chars argument, which is the set of characters to remove. .strip will remove any of the characters we provide from the beginning and end of the string.

• (Note that unlike .split, the characters don't have to occur together.)

• >

  "!!!1000.!..".strip(".!")

  Result:

  '1000'

• >

  "!10!00.".strip(".!")

  Result:

  '10!00'

• We can replace a substring with .replace(old, new).

• >

  "Hello, NAME".replace("NAME", "Amir")

  Result:

  'Hello, Amir'

• .replace replaces all instances of the old string, not just the first one.

• >

  "NAME,36,NAME".replace("NAME", "Amir")

  Result:

  'Amir,36,Amir'

• Here's a code problem:

  Write a loop that takes a comma-separated string of integers like "1,2,3", .splits them into a list, then sums them together. As a reminder, int() converts strings into numbers.

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  def sum_string(s):

  total = 0

  for value in s.split(","):

  total += int(value)

  return total

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  assert sum_string("5,3,1,2,4") == 15

  assert sum_string("1,10,100,1000") == 1111

  assert sum_string("0") == 0

  Goal:

  No errors.

  Yours:

  No errors.

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