Python之如何一次读取文件一个字符

我正在学习 python 文件处理。我试过这段代码一次读取一个字符

f = open('test.dat', 'r') 
 
while (ch=f.read(1)): 
    print ch 

为什么不工作

这是错误信息

C:\Python27\python.exe "C:/Users/X/PycharmProjects/Learning Python/01.py" 
File "C:/Users/X/PycharmProjects/Learning Python/01.py", line 4 
while (ch=f.read(1)): 
         ^ 
SyntaxError: invalid syntax 
 
Process finished with exit code 1