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In all versions of Python, boolean operators treat zero values or empty values such as "", 0, None, 0.0, [], and {} as false, while in general treating non-empty, non-zero values as true. The boolean values True and False were added to the language in Python 2.2.1 as constants (subclassed from 1 and 0 ) and were changed to be full blown ...
Python has built-in set and frozenset types since 2.4, and since Python 3.0 and 2.7, supports non-empty set literals using a curly-bracket syntax, e.g.: {x, y, z}; empty sets must be created using set(), because Python uses {} to represent the empty dictionary.
The list type is an additive monad, with nil as the monadic zero and append as monadic sum. Lists form a monoid under the append operation. The identity element of the monoid is the empty list, nil. In fact, this is the free monoid over the set of list elements.
The empty string is the unique string over Σ of length 0, and is denoted ε or λ. [25] [26] The set of all strings over Σ of length n is denoted Σ n. For example, if Σ = {0, 1}, then Σ 2 = {00, 01, 10, 11}. We have Σ 0 = {ε} for every alphabet Σ. The set of all strings over Σ of any length is the Kleene closure of Σ and is denoted Σ *.
If is a set of symbols or characters, then is the set of all strings over symbols in , including the empty string . The set V ∗ {\\displaystyle V^{*}} can also be described as the set containing the empty string and all finite-length strings that can be generated by concatenating arbitrary elements of V {\\displaystyle V} , allowing the use ...
Python uses the * operator for duplicating a string a specified number of times. The @ infix operator is intended to be used by libraries such as NumPy for matrix multiplication. [103] [104] The syntax :=, called the "walrus operator", was introduced in Python 3.8. It assigns values to variables as part of a larger expression. [105]
All values of x for which the predicate holds (is true) belong to the set being defined. All values of x for which the predicate does not hold do not belong to the set. Thus {()} is the set of all values of x that satisfy the formula Φ. [3] It may be the empty set, if no value of x satisfies the formula.
For example, in Python, raw strings are preceded by an r or R – compare 'C:\\Windows' with r'C:\Windows' (though, a Python raw string cannot end in an odd number of backslashes). Python 2 also distinguishes two types of strings: 8-bit ASCII ("bytes") strings (the default), explicitly indicated with a b or B prefix, and Unicode strings ...