Python3でTypeError: must be str, not {型}となったときの対応方法

• 環境
  • OS : macOS Mojave バージョン10.14.2
  • Python : 3.6.5

事象 : Pythonに TypeError: must be str, not list と怒られた

sys.py

import sys

print('Path : ' + sys.path)
print('Version : ' + sys.version)

$ python3 sys.py 
Traceback (most recent call last):
  File "sys.py", line 3, in <module>
    print('Path : ' + sys.path)
TypeError: must be str, not list

原因 : 文字でないものを文字で扱おうとするから

$ python3
Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 03:03:55) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> print(type(sys.path))
<class 'list'>
# ↑'str'ではなく'list'です

対応 : 文字にしてから扱う

sys.py

import sys

sys_path = str(sys.path)
print('Path : ' + sys_path)
print('Version : ' + sys.version)

$ python3 sys.py 
Path : ['/Users/mana/Dropbox/ApacheDcumentRoot', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python36.zip', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/lib-dynload', '/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages']
Version : 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 03:03:55) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)]