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Python uses the following syntax to express list comprehensions over finite lists: S = [ 2 * x for x in range ( 100 ) if x ** 2 > 3 ] A generator expression may be used in Python versions >= 2.4 which gives lazy evaluation over its input, and can be used with generators to iterate over 'infinite' input such as the count generator function which ...
Here, the list [0..] represents , x^2>3 represents the predicate, and 2*x represents the output expression.. List comprehensions give results in a defined order (unlike the members of sets); and list comprehensions may generate the members of a list in order, rather than produce the entirety of the list thus allowing, for example, the previous Haskell definition of the members of an infinite list.
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 ...
This leads to duplicating some functionality. For example: List comprehensions vs. for-loops; Conditional expressions vs. if blocks; The eval() vs. exec() built-in functions (in Python 2, exec is a statement); the former is for expressions, the latter is for statements
A language that supports the statement construct typically has rules for one or more of the following aspects: Statement terminator – marks the end of a statement; Statement separator – demarcates the boundary between two statements; need needed for the last statement; Line continuation – escapes a newline to continue a statement on the ...
Python has a syntax modeled on that of list comprehensions, called a generator expression that aids in the creation of generators. The following extends the first example above by using a generator expression to compute squares from the countfrom generator function:
For example, the sentence MOVE A B. and the sentence MOVE A TO B. perform exactly the same function, but the second makes the action to be performed clearer. Augmented assignment or compound assignment operators: For example, a += b is equivalent to a = a + b in C and similar languages, assuming a has no side effects such as if a is a regular ...
Iterators in Python are a fundamental part of the language and in many cases go unseen as they are implicitly used in the for statement, in list comprehensions, and in generator expressions. All of Python's standard built-in collection types support iteration, as well as many classes that are part of the standard library. The following example ...