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Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today. # How do I return key based on a value?

My most_courses function isn't passing, but it works in my own module.

What's up with that?

Thanks.

teachers.py
```# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.
def num_teachers(treeDict):
return len(treeDict.keys())

def num_courses(treeDict):
count = 0
for v in treeDict.values():
count += len(v)
return count

def courses(treeDict):
courseList = []
for v in treeDict.values():
for course in v:
courseList.append(course)
return((courseList))

def most_courses(treeDict):
theBigOne = max(len(value) for value in treeDict.values())
teachers = []
for key, value in treeDict.items():
if len(value) == theBigOne:
teachers.append(key)
return teachers
``` The challenge expects the method to return a single name, not a list of names. So it is expecting a string in return, not a list. If you convert your list to a string like this:

```def most_courses(treeDict):
theBigOne = max(len(value) for value in treeDict.values())
teachers = []
for key, value in treeDict.items():
if len(value) == theBigOne:
teachers.append(key)
return ''.join(teachers)
```

Or not make it a list in the first place like this:

```def most_courses(treeDict):
theBigOne = max(len(value) for value in treeDict.values())
teacher = ''
for key, value in treeDict.items():
if len(value) == theBigOne:
teacher = key
return teacher
```

Then your code will be accepted.