Python文件打开方式实例详解【a、a+、r+、w+区别】

fd = open("1.txt",'w+')
fd.write('123')
fd = open("1.txt",'r+')
fd.write('456')
fd = open("1.txt",'a+')
fd.write('789')

> fd=open(r'f:\mypython\test.py','w') #只读方式打开，读取报错
> fd.read()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
IOError: File not open for reading
> fd=open(r'f:\mypython\test.py','a')#附加写方式打开，读取报错
> fd.read()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
IOError: File not open for reading
>

> fd=open(r'f:\mypython\test.py','a+')
> fd.write('123')
> fd.read()
> fd.close()

> fd=open(r'f:\mypython\test.py','a+')
> fd.seek(0)
> fd.read()
'123'#顺利读出

> fd=open(r'f:\mypython\test.py','w+') #清空内容，重新写入
> fd.write('456')
> fd.flush()#确定写入，此时文件内容为“456”
> fd.read()
'' #读出空

> fd.close()
> fd=open(r'f:\mypython\test.py','a+')
> fd.read()
'456'
> fd.close()
> fd=open(r'f:\mypython\test.py','r+')
> fd.read()
'456'
> fd.close()
> fd=open(r'f:\mypython\test.py','r')
> fd.read()
'456'
> fd.close()
> fd=open(r'f:\mypython\test.py','U')
> fd.read()
'456'

> fd=open(r'f:\mypython\test.py','w+')
> fd.write('456')
> fd.seek(0)
> fd.read()
'456'

with open('/Users/michael/test.txt', 'w') as f:
  f.write('Hello, world!')