Python函数混乱

我有一个简单的函数调用,如下所示：

fname = 'hello.txt'
readwrite('xx'+fname,datalist)

我面临的问题是,当我在函数定义中打印文件名参数值时,我得到hello.txt而不是xxHello.txt – 这是一个奇怪的事情,当我从commadline做同样的事情时我没想到,对于一个示例函数,它工作正常.
我想知道我在那里失踪了什么.

这是代码：

def readwrite(fileName,list):
    print 'arg file=',filename
    curdir = os.getcwd();
    fullpath = os.path.join(curdir,filename);
    print('full path calculated as: '+fullpath);
    fileExist = os.path.exists(fullpath);
    if(fileExist):
        print 'file exists and opening in 'arw'mode'
        fiel = open(fileName,'arw')    # valid only if exists
    else:
        print "file doesnt exist; opening in 'w'mode"
        fiel = open(fileName,'w')      # if it doesnt exist,we cant open it for reading as nothing to read.

    for line in list:
        fiel.write('n'+line)

    print 'position of new pointer = ',fiel.tell()

– 调用函数的主代码：

filename = 'put.txt'
strList = ['hello','how','are','you']
readwrite(('xx'+filename),strList);

– fn def print’arg file =’中的第二行,filename打印hello.txt而不是xxHello.txt
这是我的困惑,为什么它表现得很好,或者我做错了什么.