Powerful and elegant list derivation expressions in Python

The derivation of the expression is actually to simplify some circular judgment operation, etc.

How many ways can you generate a list of number 1-10?

>>> L = [1, 2, 3, 4, 5, 6, 7, 8, 9, ten ]>>> l[1, 2, 3, 4, 5, 6, 7, 8, 9, ten]

>>> L = [] for in range (1, one ): ...      . >>> l[1, 2, 3, 4, 5, 6, 7, 8, 9, >>>

>>> L = Range (1, one )>>> l[1, 2, 3, 4, 5, 6, 7, 8, 9, ten]

Now look at the derivation expression

 for  in range (1, one )]>>> a[1, 2, 3, 4, 5, 6, 7, 8, 9, ten]

Some people, may say, direct range (1, 11) just fine, superfluous, if we're going to sift through the odd number?

Of course, range can still do the following:

>>> Range (1, 2 ) [1, 3, 5, 7, 9]

That, if you want to get even, you need to traverse each item, judge

>>> a = [] for in range (1, one ): ...      . if x% 2 = = 0:              ... >>> >>> a[2, 4, 6, 8, ten]

He is equivalent to the following derivation expression:

 for inch if x% 2 = = 0]>>> b[2, 4, 6, 8, ten]

A word.

Generate a coordinate system?

>>> dot = [(x, Y) forXinchRange (1, 10) forYinchRange (1, 10 ) ]>>>dot[(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (1, 7), (1, 8), (1, 9), (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2), 7), (2, 8), (2, 9), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6), (3, 7), (3, 8), (3, 9), (4, 1), (4, 2), (4, 3),  ), (4, 5), (4, 6), (4, 7), (4, 8), (4, 9), (5, 1), (5, 2), (5, 3), (5), (4, 5), (5, 5), (6, 5), (7, 5), (8, 5), (9, 6), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6), (6, 7), (6, 8), (6, 9), (7), (1, 7), (2, 7), (3, 7), (4, 7), (5, 7), (6, 7), (  7, 8), (7, 9), (8, 1), (8, 2), (8, 3), (8, 4), (8, 5), (8, 6), (8, 7), (8, 8), (8, 9), (9, 1), (9, 2), (9, 3), (9), 5), (9, 6), (9, 7), (9, 8), (9, 9)]>>>

Equivalent to the following 2 heavy loops:

>>> dot = []>>> forXinchRange (1, 10 ):...      forYinchRange (1, 10): ... dot.append ((x, y)) ...>>>dot[(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (1, 7), (1, 8), (1, 9), (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2), 7), (2, 8), (2, 9), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6), (3, 7), (3, 8), (3, 9), (4, 1), (4, 2), (4, 3),  ), (4, 5), (4, 6), (4, 7), (4, 8), (4, 9), (5, 1), (5, 2), (5, 3), (5), (4, 5), (5, 5), (6, 5), (7, 5), (8, 5), (9, 6), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6), (6, 7), (6, 8), (6, 9), (7), (1, 7), (2, 7), (3, 7), (4, 7), (5, 7), (6, 7), (  7, 8), (7, 9), (8, 1), (8, 2), (8, 3), (8, 4), (8, 5), (8, 6), (8, 7), (8, 8), (8, 9), (9, 1), (9, 2), (9, 3), (9), 5), (9, 6), (9, 7), (9, 8), (9, 9)]>>>

Generate a list of incrementing strings:

>>> ['The number:%s'% n forNinchRange (1, 10 ) ]['The number:1','The number:2','The number:3','The number:4','The number:5','The number:6','The number:7','The number:8','The number:9']

Ask for 1-9 square of each number

 for  in range (1, ten ) [1, 4, 9, (+), +, +, +, Bayi]

Wrap a layer in a dictionary, and the same key will overwrite the previous

 for inch  for  in range (1, 5 )] {1:4, 2:4, 3:4, 4:4} for in range (1, 5 )]  [(1, 1), (1, 2), (1, 3), (1, 4), (2, 1), (2, 2), (2, 3), (2, 4), (3, 1), (3, 2), (3, 3), (3, 4), (4, 1), (4), 3), (4, 4)]

List of references, with JavaScript type:

>>> L = ['my','name',' is','GHOSTWU' ]>>>l['my','name',' is','GHOSTWU']>>> A =L>>> A[3] ='Wukong'>>>l['my','name',' is','Wukong']>>>dela>>>l['my','name',' is','Wukong']>>>Atraceback (most recent): File"<stdin>", Line 1,inch<module>Nameerror:name'a'  is  notdefined>>>

Del A, a reference to the list is deleted, similar to the PHP garbage collection mechanism, two variables point to a list, delete one, but the other points to the list.

>>> a = [10, 20, 30 ]>>> B =a>>>b[10, 20, 30]>>>dela>>>Atraceback (most recent): File"<stdin>", Line 1,inch<module>Nameerror:name'a'  is  notdefined>>>b[10, 20, 30]>>>

Del a[], this refers to emptying the list

>>> a = [All, ten, ]>>> b = adel  a[:]>>> >>>  A[]>>> b[]

Powerful and elegant list derivation expressions in Python