Bytes and Strings.md

Bytes and Strings

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Strings

• represent sequences of characters (Unicode code points)

• are immutable, which requires that operations on them create new strings

• implemented using the Type str

• can be created by enclosing text in 'single' or "double" quotes (literals)

• the length can be determined by len(string)

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Escape Sequences

• strings can contain characters which are difficult to type

• escape sequences allow to represent them using ASCII characters

• always start with a backslash and can be disabled by writing r"string"

Escape sequence	Result
\n	ASCII Linefeed
\t	ASCII Horizontal Tab
\\\\	\\
\"	" (works with single quotes too)

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Operators

• strings can be concatenated by adding them using +

• doing so with str.join(strings) is more efficient when concatenating many strings

• using * with a string and an integer repeats the string

• == checks whether two strings are equal

  (!= checks the opposite)

• do not use the is operator to perform value comparisions!

    # both are equal to "Hello World!"
    "Hello" + " " + "World!"

    " ".join(["Hello", "World"])

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Substrings

• substrings can be accessed using string[start:end] with end defaulting to start + 1

• writing : without specifying a value defaults to the start and end of the string

    # returns "Hello"
    "Hello World!"[0:5]
    "Hello World!"[:5]

    # returns " "
    "Hello World!"[5]

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Splitting

• str.partition(seperator) splits the string into the part before the first seperator, the seperator and the part after the seperator

• str.split(seperator) splits the string into a list of substrings at the seperator (opposite to str.join)

    # returns ("Hello", " ", "World!")
    before, seperator, after = \
      "Hello World!".partition(" ")

    # returns ("Hello World!", "", "")
    "Hello World!".partition("not found")

    # returns ["Hell", " W", "rld!"]
    "Hello World!".split("o")

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Formatting

• strings can be filled with values by using str.format(*args, **kwargs)

• values to be filled in are represented using curly brackets ({}) containing the index or name of the value to be filled in

• literals perfixed with f can contain variables

    # both are equal to "Hello World!"
    "{greeting} {0}!".format("World", greeting="Hello")

    greeted = "World"
    f"Hello {greeted}!"

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Bytes

• similar to strings, but dont have to contain valid text

• implemented using the Type bytes

• literals are prefixed with b

• can be transformed into strings using bytes.decode(encoding)

• can be created from strings using str.encode(encoding)

b"Hello W\xc3\xb6rld!".decode("utf8") == "Hello Wörld!"
b"Hello W\xc3\xb6rld!" == "Hello Wörld!".encode("utf8")