TypeError: 'int' object is not subscriptable

[ruimmpires]

the code works fine!
However I am a newbie and tried to make editing the training data a bit more easy so I've created a file training_data.data as:
Green,3,Apple
Yellow,3,Apple
Red,1,Grape
Red,1,Grape
Yellow,3,Lemon
and then import this with:
import pandas as pd
training_data = pd.read_csv('training_data.data', header=-1)

and now I gut the error TypeError: 'int' object is not subscriptable.

[ruimmpires]

also tried to force the dimension to be integer, but now get many weird errors:
training_data = pd.read_csv('training_data.data', dtype={"diameter": np.int32})
header = training_data.columns

The training_data.data is now:
"color","diameter","label"
'Green',3,'Apple'
'Yellow',3,Apple'
'Red',1,'Grape'
'Red',1,'Grape'
'Yellow',3,'Lemon'

Traceback (most recent call last):
File "/home/rpires/.local/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 2656, in get_loc
return self._engine.get_loc(key)
File "pandas/_libs/index.pyx", line 108, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 1601, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 1608, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "decision_tree_withCSVdata.py", line 410, in
my_tree = build_tree(training_data)
File "decision_tree_withCSVdata.py", line 318, in build_tree
gain, question = find_best_split(rows)
File "decision_tree_withCSVdata.py", line 247, in find_best_split
n_features = len(rows[0]) - 1 # number of columns
File "/home/rpires/.local/lib/python3.7/site-packages/pandas/core/frame.py", line 2927, in getitem
indexer = self.columns.get_loc(key)
File "/home/rpires/.local/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 2658, in get_loc
return self._engine.get_loc(self._maybe_cast_indexer(key))
File "pandas/_libs/index.pyx", line 108, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 1601, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 1608, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 0