Python學習筆記7-進階迭代器

標籤：

將任何字串作為python運算式求值：

eval()方法：

eval(source[, globals[, locals]]) -> value
Evaluate the source in the context of globals and locals.
The source may be a string representing a Python expression
or a code object as returned by compile().
The globals must be a dictionary and locals can be any mapping,
defaulting to the current globals and locals.
If only globals is given, locals defaults to it.

用法：

>>> eval(‘1+1==2‘)True>>> eval(‘1+1==3‘)False>>> eval(‘9567+1085 == 10652‘)True>>> eval(‘"A"+"B"‘)‘AB‘>>> eval(‘"MARK".translate({65:79})‘)‘MORK‘>>> eval(‘"AAAAA".count("A")‘)

 

>>> eval("x*5",{}, {})Traceback (most recent call last):  File "<pyshell#120>", line 1, in <module>    eval("x*5",{}, {})  File "<string>", line 1, in <module>NameError: name ‘x‘ is not defined>>> eval("x*5",{"x":x},{})25>>> import math>>> eval("math.sqrt(x)",{"x":x},{})Traceback (most recent call last):  File "<pyshell#123>", line 1, in <module>    eval("math.sqrt(x)",{"x":x},{})  File "<string>", line 1, in <module>NameError: name ‘math‘ is not defined

 註：

給eval()函數傳遞的第二、第三個參數擔當了求值運算式是全域和局部名字空間的角色

eval()是不安全的，為了安全的求值不受信任的運算式，需要定義一個將"__builtins__"映射為none的全域名字空間字典。在內部，“內建”函數包含在一個叫“__builtins__"的偽模組內。

 

re.findall() -- 返回字串中所有字母

set() --  返回字串中所有不同的字母

 

Python學習筆記7-進階迭代器