Python for Programmers: Basic Data Types

• Python's basic data types include integers, floating point numbers, strings, and booleans. These mostly work in familiar ways, so we'll only discuss them briefly.

• Python's Boolean values are True and False. Note that they're not true and false! Normally, UpperCamelCased names indicate classes in Python, but this is an exception. It's an inconsistency on Python's part.

• >

  1 == 1

  Result:

  True

• >

  2 > 3

  Result:

  False

• Many other languages, most notably JavaScript, use C-style logical operators. In those languages, && means "and", || means "or", and ! means "not". Python's operators are different: it uses the words and, or, and not.

• >

  True and True

  Result:

  True

• >

  1 + 1 == 2 and 2 + 2 == 3

  Result:

  False

• >

  False or True

  Result:

  True

• >

  1 > 2 or 3 == 4

  Result:

  False

• >

  not True

  Result:

  False

• >

  not not True

  Result:

  True

• Although Python doesn't use the more common && operator style, its precedence rules match most other languages. As an example, not x or y is equivalent to (not x) or y.

• >

  not True or True

  Result:

  True

• >

  (not True) or True

  Result:

  True

• >

  not (True or True)

  Result:

  False

• We can use the bool built-in function to convert other types into booleans. Any zero number (like 0 or 0.0) converts to False, and any non-zero number converts to True.

• >

  bool(1.5)

  Result:

  True

• >

  bool(0.0)

  Result:

  False

• >

  bool(37)

  Result:

  True

• >

  bool(0)

  Result:

  False

• Strings work similarly. Empty strings convert to False and non-empty strings convert to True.

• >

  bool("abc def")

  Result:

  True

• >

  bool("")

  Result:

  False

• Note that whitespace characters are still characters. A string with only whitespace converts to True.

• >

  bool(" ")

  Result:

  True

• We can use any value in boolean expressions. For example, not value works even if value isn't a boolean. In that case, Python uses the bool built-in to automatically convert value into a boolean. It's as if we did not bool(value). (In a future lesson, we'll come back to this idea of "truthy" and "falsey" values in more detail.)

• >

  not " "

  Result:

  False

• Python distinguishes between integers and floating point numbers. Integers are whole numbers: positive, negative, and 0. Floats contain decimal points, like "real numbers" in a math class. However, floats don't guarantee precision. A future lesson will cover floating point precision in more detail.

• Any operation involving a float returns a float.

• >

  2.0 * 3.0

  Result:

  6.0

• Combining integers and floats gives us a float, even if the result is a round number.

• >

  3 * 1.5

  Result:

  4.5

• >

  5 * 2.0

  Result:

  10.0

• >

  10 + 3

  Result:

  13

• Python has the usual operators like +, *, etc. It also has a convenient exponentiation operator, **, which many languages lack.

• >

  3**2

  Result:

  Run Code

• >

  2**3

  Result:

  8

• We can compare integers against floats, like some_int == some_float. However, floating point imprecision means that this is much more subtle than it seems. We'll see more details of floating point imprecision in a future lesson.

• >

  2 == 2.0

  Result:

  True

• Python has special syntax for scientific notation with an explicit exponent. For example, 2.1e3 is equivalent to 2.1 * (10**3), or 2.1 * 1000.

• >

  2.1e3

  Result:

  2100.0

• This syntax always gives us floats. The 2e2 in the next example doesn't include a decimal point, but it's equivalent to 2.0 * 100.

• >

  2e2

  Result:

  200.0

• Scientific notation also allows negative exponents. 1.2e-1 gives the equivalent of 1.2 * (10**-1), or 1.2 / 10

• >

  1.2e-1

  Result:

  0.12

• 0.12 and .12 are equivalent in Python, so either one is a correct answer for that code example.

• >

  0.12 == .12

  Result:

  Run Code

• Strings go inside single or double quotes. (Though Python also has some additional string syntax that we'll see later.) We can get the length of a string with the len function.

• >

  message = "Hello"
  len(message)

  Result:

  5

• We can combine strings with +.

• >

  name = "Amir"
  greeting = "Hello, " + name + "!"
  greeting

  Result:

  'Hello, Amir!'

• We can escape characters inside of strings with \, which makes it clear that we're including a special character. For example. "\"" is a string containing a single character, a double quote.

• >

  len("\"")

  Result:

  1

• In this case, it'd be better to use a single-quoted string so we don't have to escape the " character at all.

• >

  '"' == "\""

  Result:

  Run Code

• Those are the basic types! Now we can move on to the deeper details that make Python Python.