A: set of derivations
1, with iterables to create (generate) expression set is called the set of derivations
2, Grammar
Variable in the expression for {iterables [if truth expression]}
Note: [] brackets part may be omitted
Example:
L = [2,3,5,7,3,5,7,11]
S = {x**2 for x in L}
Analysis: First, the definition of a case table, for use inside the loop through the list of elements, then the x value is then passed to expression, which calculates the square element, and finally to remove duplicate data converted into a set of printed output. FIG code is as follows:
3, the derivation of a set of nested
Rules and list comprehensions same. Example:
S = ‘ABC’
n = ‘123’
s1 = {x + y for x in ‘ABC’ for y in ‘123’}
Analysis: two strings are defined and assigned to loop through the inside of the string value S, the first element of the S x expression pass, and then traversing n elements, the first element of y n pass. expression, expressions adding the elements, then y then passed to the second element of expression, be added to the first element of s. Until complete traversal element n, then S is traversing the second result value below ......
4. Exercise
Simulation of a student in class online system, known class list of students randomly print the student's name be named, and whether the student has been attending, enter 'y' representatives have to, on behalf of the other inputs are not present. Printing not yet reached the end of the roll call list.
Two: a fixed set (frozenset)
Set 1, a fixed set of immutable, disorder, contains a unique element
2, a fixed set of keys of a dictionary may also be used as a value (element) set
3, format:
Create a fixed set of empty:
fs = frozenset()
Create a non-empty set of fixed
Fs = frozenset([2,3,5,7])
Constructor:
Frozenset()
Frozenset (iterables) set with the same function, a fixed set of returns
4, the following arithmetic operation :( fixed rule set is equivalent to the usage of the set in)
& Intersection
| Union
-Complement
^ Symmetrical complement
<>= < <= == !=
In / not in
5, a fixed set of methods:
The method corresponds to the set of all sets of methods modified to remove
to sum up:
相比较其它语句，固定集合用的很少，我们一般用集合，这章节的内容很简单，大家只要记住集合的推导式就行。
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