NameError: name 'print_models' is not defined

[OctopusLian]

运行8-16print_models.py程序

import printing_functions

unprinted_designs = ['iphone case', 'robot pendant', 'dodecahedron']
completed_models = []

print_models(unprinted_designs, completed_models)
show_completed_models(completed_models)

报错信息

Traceback (most recent call last):
  File "/home/zoctopus/code/github_organization/programming-book-practice/Python-Crash-Course-Homework/chapter08/print_models.py", line 6, in <module>
    print_models(unprinted_designs, completed_models)
NameError: name 'print_models' is not defined

思考

按照书上讲解，import文件名后，这个被引入文件里的所有定义的函数都是通用的。
为什么报not defined的错误呢？