TypeError: a bytes-like object is required, not 'str'

[UltimatePancake]

 I  ~/.config/habitica  habitica --debug status                                                                                                                                                                            3359ms
DEBUG:root:Command line args: {'--version': 'False', '--help': 'False', '<command>': 'status', '<args>': '[]', '--difficulty': 'easy', '--verbose': 'False', '--debug': 'True', '--checklists': 'False'}
DEBUG:root:Loading habitica auth data from /home/pancake/.config/habitica/auth.cfg
DEBUG:root:Loading cached config data (/home/pancake/.config/habitica/cache.cfg)...
DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): habitica.com
DEBUG:requests.packages.urllib3.connectionpool:https://habitica.com:443 "GET /api/v3/user HTTP/1.1" 200 None
DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): habitica.com
DEBUG:requests.packages.urllib3.connectionpool:https://habitica.com:443 "GET /api/v3/groups?type=party HTTP/1.1" 200 206
DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): habitica.com
DEBUG:requests.packages.urllib3.connectionpool:https://habitica.com:443 "GET /api/v3/groups/523d2eb1-9944-4286-a9a5-c4493fbe0a0e HTTP/1.1" 200 None
INFO:root:Updating quest information...
DEBUG:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): habitica.com
DEBUG:requests.packages.urllib3.connectionpool:https://habitica.com:443 "GET /api/v3/content HTTP/1.1" 200 None
DEBUG:root:	On a boss/hp type of quest
DEBUG:root:Updating (and caching) config data (/home/pancake/.config/habitica/cache.cfg)...
DEBUG:root:Loading cached config data (/home/pancake/.config/habitica/cache.cfg)...
Traceback (most recent call last):
  File "/home/pancake/.local/bin/habitica", line 13, in <module>
    habitica.cli()
  File "/home/pancake/.local/lib/python3.6/site-packages/habitica/core.py", line 335, in cli
    quest_title=str(quest_title))
  File "/home/pancake/.local/lib/python3.6/site-packages/habitica/core.py", line 115, in update_quest_cache
    cache.write(f)
  File "/usr/lib/python3.6/configparser.py", line 916, in write
    self._defaults.items(), d)
  File "/usr/lib/python3.6/configparser.py", line 923, in _write_section
    fp.write("[{}]\n".format(section_name))
TypeError: a bytes-like object is required, not 'str'

[KIAaze]

I had the same issue. It only seems to be happening when cache.cfg is missing, i.e. to any new user.
I fixed it by simply disabling binary writing. Hopefully that does not break anything else, in particular any unicode encoded tasks or similar... I failed to make configparser work with unicode section, key, values.
It works fine for me so far.

Here is a patch:

diff --git a/habitica/core.py b/habitica/core.py
index 980dfad..9c2c18d 100755
--- a/habitica/core.py
+++ b/habitica/core.py
@@ -111,7 +111,7 @@ def update_quest_cache(configfile, **kwargs):
     for key, val in kwargs.items():
         cache.set(SECTION_CACHE_QUEST, key, val)
 
-    with open(configfile, 'wb') as f:
+    with open(configfile, 'w') as f:
         cache.write(f)
 
     cache.read(configfile)

[KIAaze]

Already fixed by this pull request #36