Binding a dataframe to a variable in a for-loop converts it into a tuple?

Sorry if this is basic but I am new to python.

I was experimenting with creating plots in pandas through a for loop when I got AttributeError: 'tuple' object has no attribute 'plot'.

Looking at my code, I found out that assigning a dataframe to a variable converts it into a tuple. See below:

import seaborn as sns
flowers = sns.load_dataset('iris')

for k in flowers['species'].unique():
    print('1. ', k)
    print('2. ', type(k))
    print('3. ', type(flowers[flowers['species'] == k]))
    t = flowers[flowers['species'] == k],
    print('4. ', type(t))

Output:

1.  setosa
2.  <class 'str'>
3.  <class 'pandas.core.frame.DataFrame'>
4.  <class 'tuple'>
1.  versicolor
2.  <class 'str'>
3.  <class 'pandas.core.frame.DataFrame'>
4.  <class 'tuple'>
1.  virginica
2.  <class 'str'>
3.  <class 'pandas.core.frame.DataFrame'>
4.  <class 'tuple'>

This doesn’t happen if I do the same thing outside the for-loop.

print(type(flowers[flowers['species'] == 'setosa']))
o = flowers[flowers['species'] == 'setosa']
print(type(o))

Output:

<class 'pandas.core.frame.DataFrame'>
<class 'pandas.core.frame.DataFrame'>

Can someone explain to me python’s assignment logic here? Why is this happening?

Answer

In the for loop,

    t = flowers[flowers['species'] == k],

you add an extra comma , at the end, and that results:

t = x,
x = flowers[flowers['species'] == k]

# t is a tuple with one element

tuple defination:

class tuple([iterable])
Tuples may be constructed in a number of ways:

Using a pair of parentheses to denote the empty tuple: ()
Using a trailing comma for a singleton tuple: a, or (a,)
Separating items with commas: a, b, c or (a, b, c)
Using the tuple() built-in: tuple() or tuple(iterable)