This optimization removes invariant subexpressions from the body of a loop.
此优化将不变量子表达式从循环体中移除。
And the subexpressions can be combined using the and, or, and not logical operators.
而子表达式又可使用and、or和not逻辑运算符组合起来。
When all parenthetical subexpressions have been evaluated, the rest of the expression is evaluated.
所有括号内的子表达式都求值完毕后，表达式的其它部分再求值。
Sets of parentheses match "subexpressions" that can potentially make up part of the replacement pattern.
括号对与可能组成部分替换模式的“子表达式”匹配。
This optimization allows the compiler to store frequently used variables and subexpressions in registers;
此优化允许编译器将常用变量和子表达式存储在寄存器中；
It can be composed of multiple subexpressions that use the different relational operators supported in Python.
它可以包括多个使用Python中支持的不同关系运算符的子表达式。
For global common subexpression optimization, the compiler searches entire functions for common subexpressions.
对于全域通用子运算式最佳化，编译器会搜寻整个函式中有没有通用子运算式。
For local common subexpression optimization, the compiler examines short sections of code for common subexpressions.
对于区域通用子运算式最佳化，编译器会检查程序码的短区段中有没有通用子运算式。
Do not use an increment or decrement operator on the same object in more than two subexpressions of the same expression.
一个表达式里，不要在两个或更多的子表达式中对同一对象做自增或自减操作。
The first of these "non-reference" child subexpressions just says "match something that looks like HTTP or that looks like FTP or...".
第一个“非引用”子表达式只表示“查找类似于http或ftp或其它值的字符串”。
First notice that this subexpression is itself composed of two child subexpressions, with some stuff in the middle that is not part of any child subexpression.
首先，请注意这个子表达式本身由两个子表达式组成，两者之间的字符并不属于任何一方。
The value of an expression depends on how the subexpressions are grouped. For example, in the following expression, a purely left-to-right evaluation yields 20.
表达式的值取决于其子表达式如何分组。例如，下面的表达式，如果纯粹从左向右计算，结果为20。
The value of an expression depends on how the subexpressions are grouped. For example, in the following expression, a purely left-to-right evaluation yields 20.
表达式的值取决于其子表达式如何分组。例如，下面的表达式，如果纯粹从左向右计算，结果为20。
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