求下列代码有何问题？

import os
def get_text(f):
    with open(f) as file:
        text = file.read()
    return text
print(get_text(习题.txt))

Traceback (most recent call last):
  File "/Users/mac/Desktop/1.py", line 6, in <module>
    print(get_text(习题.txt))
NameError: name '习题' is not defined

如下：

import os
def get_text(f):
    with open(f) as file:
        text = file.read()
    return text
print(get_text("习题.txt"))