Python新人，在做一个小软件，用到了pdfminer这个包，我在Python文件中用到os.system()函数：
os.system('pdf2txt.py -o "E:\PDF\output.txt" "E:\PDF\A Functional Genetic Approach Identifies the PI3K Pathway as a Major Determinant of Trastuzumab Resistance in Breast Cancer.pdf"')
"E:\PDF\A Functional Genetic Approach Identifies the PI3K Pathway as a Major Determinant of Trastuzumab Resistance in Breast Cancer.pdf"这个路径要用双引号表示，现在我想定义一个变量strSource，令strSource ="E:\PDF\A Functional Genetic Approach Identifies the PI3K Pathway as a Major Determinant of Trastuzumab Resistance in Breast Cancer.pdf"，再代入os.system()中，结果strSource中的字符串的引号变成单引号了，导致无法生成output.txt，不知道谁知道怎样把Python中字符串默认的单引号转换为双引号。
