小编Ali*_*ehi的帖子

我找到了一个简单的语法来开始学习ANTLR.我把它放在myGrammar.g文件中.这是语法:

grammar myGrammar;
/* This will be the entry point of our parser. */
eval
    :    additionExp
    ;

/* Addition and subtraction have the lowest precedence. */
additionExp
    :    multiplyExp 
         ( '+' multiplyExp 
         | '-' multiplyExp
         )* 
    ;

/* Multiplication and division have a higher precedence. */
multiplyExp
    :    atomExp
         ( '*' atomExp 
         | '/' atomExp
         )* 
    ;
atomExp
    :    Number
    |    '(' additionExp ')'
    ;

/* A number: can be an integer value, or a decimal value */
Number …

我想在Python中创建一个目录.

这是我的代码:

dl_path = "~/Downloads/PDMB"

def main():
    if not os.path.exists(dl_path):
        print "path doesn't exist. trying to make"
        os.makedirs(dl_path)

if __name__ == '__main__':
    main()

我希望pdmb在Download文件夹中$HOME(顺便说一句,我的操作系统是Ubuntu),但它使Home/Downloads/pdmb与我的代码所在的文件夹相同.

我该怎么办？