ファイルの上書きができない。

with open('sil01python.csv', 'r',encoding = 'utf-8') as f:
    t = ''
    for line in f:
        t += line.replace("<br"," ")

    with open('sil01python.csv','w',encoding='utf-8') as writing:
        writing.write(t)

以下のエラーが出ました。

C:\Users\Yo\Desktop\excel>python python.py
Traceback (most recent call last):
  File "python.py", line 10, in <module>
    with open('sil01python.csv','w',encoding='utf-8') as writing:
PermissionError: [Errno 13] Permission denied: 'sil01python.csv'