python內建eval, exec 和exec函數的用法

函數原型：

    eval(str [,globals [,locals ]]) 

可以用來將字串str當成有效Python運算式來求值，並返回計算結果。同樣地, exec語句將字串str當成有效Python代碼來執行。最後，execfile(filename [,globals [,locals ]])函數可以用來執行一個檔案。

例如：現在有一個字串,形如字典值dict值，需要把它轉換成python 的 dict 資料，我們可以用eval()函數來轉換，代碼如下

"{
'Define1':[[63.3,0.00,0.5,0.3,0.0],[269.3,0.034,1.0,1.0,0.5],[332.2,0.933,0.2,0.99920654296875,1],[935.0,0.990,0.2,0.1,1.0]],
'Define2':[[63.3,0.00,0.5,0.2,1.0],[269.3,0.034,1.0,0.3,0.5],[332.2,0.933,0.2, 0.4,0.6],[935.0,0.990,1.0, 0.5,0.0]],
}"

#-------------------------------------------------------------------------------# Name:        模組1# Purpose:## Author:      User## Created:     11/10/2012# Copyright:   (c) User 2012# Licence:     <your licence>#-------------------------------------------------------------------------------def main():    dictString = "{'Define1':[[63.3,0.00,0.5,0.3,0.0],[269.3,0.034,1.0,1.0,0.5],[332.2,0.933,0.2,0.99920654296875,1],[935.0,0.990,0.2,0.1,1.0]],'Define2':[[63.3,0.00,0.5,0.2,1.0],[269.3,0.034,1.0,0.3,0.5],[332.2,0.933,0.2, 0.4,0.6],[935.0,0.990,1.0, 0.5,0.0]],}"    dict = eval(dictString)    print "keys:", dict.keys()    print "Define1 value ", dict['Define1']if __name__ == '__main__':    main()