Function not defined.

'''
Server restart initiated ...
Traceback (most recent call last):
  File "d:\muddev\evennia\evennia\commands\cmdsethandler.py", line 174, in import_cmdset
    module = import_module(modpath, package="evennia")
  File "C:\Programming\Python3\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File ".\commands\default_cmdsets.py", line 18, in <module>
    from commands import command
  File ".\commands\command.py", line 10, in <module>
    from world.skillsets import training
  File "D:\muddev\hecate\world\skillsets.py", line 7, in <module>
    rb = skill_level(i, 'easy')
NameError: name 'skill_level' is not defined

Compile/Run error when loading cmdset 'commands.default_cmdsets.SessionCmdSet'.",
(Traceback was logged 19-08-08 03:54:57-04)

Error encountered for cmdset at path 'commands.default_cmdsets.SessionCmdSet'.
Replacing with fallback 'evennia.commands.default.cmdset_session.SessionCmdSet'.
 ... Server restarted.
'''

# In mygame\world\skillsets.py
easy_rb = []
average_rb = []
difficult_rb = []
impossible_rb = []

for i in range(1, 1_001):
    rb = skill_level(i, 'easy')
    easy_rb.append(rb)

    rb = skill_level(i, 'average')
    average_rb.append(rb)

    rb = skill_level(i, 'difficult')
    difficult_rb.append(rb)

    rb = skill_level(i, 'impossible')
    impossible_rb.append(rb)

def skill_level(self, rank, difficulty):
    '''
    RANK += RANK BONUS PER RANK
    --------------------------
    1 to 10 += 3
    11 to 30 += 2
    31 to 50 += 1
    51 to 100 += 0.5
    101 to 150 += 0.25
    151 to 200 += 0.125
    201 to 500 += 0.0625
    501 to 1,000 += 0.025
    1,001 to infinity += 0.01
    '''
    #Temp Values
    rb = 0
    rank = 100

    #Formula
    if rank:
        r = rank if rank < 10 else 10
        rb += (3 * r)
        if rank >= 11:
            r = rank - 10 if rank < 30 else 10
            rb += (2 * r)
            if rank >= 31:
                r = rank - 30 if rank < 50 else 20
                rb += (1 * r)
                if rank >= 51:
                    r = rank - 50 if rank < 100 else 50
                    rb += (0.5 * r)
                    if rank >= 101:
                        r = rank - 100 if rank < 150 else 50
                        rb += (0.25 * r)
                        if rank >= 151:
                            r = rank - 150 if rank < 200 else 50
                            rb += (0.125 * r)
                            if rank >= 201:
                                r = rank - 200 if rank < 500 else 300
                                rb += (0.0625 * r)
                                if rank >= 501:
                                    r = rank - 500 if rank < 1000 else 500
                                    rb += (0.025 * r)
                                    if rank >= 1001:
                                        r = rank - 1000
                                        rb += (0.01 * r)
        '''
        15% RB loss per difficulty.
        At rank 100:
        Easy(100%) 115 RB
        Average(85%) 97.75 RB
        Difficult(70%) 80.5 RB
        Impossible(55%) 63.25 RB
        '''
        if difficulty == 'easy':
            rb *= 1
        elif difficulty == 'average':
            rb *= 0.85
        elif difficulty == 'difficult':
            rb *= 0.7
        elif difficulty == 'impossible':
            rb *= 0.55
        return rb # Return if any rank.
    return None # Return if no rank.