Python is a lovely and interesting dynamic language, powerful and efficient, the syntax is beautiful and simple, let's play the lovely side of it: List resolution and generator expressions.
List resolution:
Syntax: [Expr for Iter_var in iterable] or [expr for Iter_var in iterable if COND_EXPR]
Description
The first syntax: first iterate over all the content in iterable, each iteration, put the corresponding content in the iterable in the Iter_var, and then apply the Iter_var content in the expression, and finally generate a list with the calculated value of the expression.
The second kind of syntax: added the judgment statement, only satisfies the condition the content to put the corresponding content in the iterable in the Iter_var, then applies the Iter_var content in the expression, finally uses the expression the computation value to produce a list.
Example:
>>> [i + 1 for I in range (10)]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> [i + 1 for I in range (ten) if I% 2]
[2, 4, 6, 8, 10]
How, very convenient, very natural.
Builder expression:
Syntax: (expr for Iter_var in iterable) or (expr for iter_var in iterable if cond_expr)
Description: List parsing is introduced in the earlier Python version (like the 2.0 version), the generator expression is the new content introduced in 2.4, which is similar to the syntax of list parsing, but the advantage of the generator expression is reflected in the large amount of data processing, because it uses better memory, More efficient, it doesn't create a list, just returns a generator. Of course, list parsing is not abandoned.
Example:
>>> (i + 1 for I in range (a) if I% 2)
<generator Object <genexpr> at 0x011dc5d0>
>>> g = (i + 1 for I in range (a) if I% 2)
>>> L = []
>>> for J in G:
L.append (j)
>>> L
[2, 4, 6, 8, 10]
As you can see from the above, list parsing and builder expression syntax are very similar, but in essence they are quite different.
Python is powerful, beautiful, efficient, concise and interesting, and hopefully more people will come to know it.
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