How to identify a pandas column is a list

Question

I want to identify if a column in pandas is a list (in each row).

df=pd.DataFrame({'X': [1, 2, 3], 'Y': [[34],[37,45],[48,50,57]],'Z':['A','B','C']})

df
Out[160]: 
   X             Y  Z
0  1          [34]  A
1  2      [37, 45]  B
2  3  [48, 50, 57]  C

df.dtypes
Out[161]: 
X     int64
Y    object
Z    object
dtype: object

Since the dtype of strings is "object", I'm unable to distinguish between columns that are strings and lists (of integer or strings).

How do I identify that column "Y" is a list of int?

Answer 1

You can use applymap, compare and then add all for check if all values are Trues:

print (df.applymap(type))
               X               Y              Z
0  <class 'int'>  <class 'list'>  <class 'str'>
1  <class 'int'>  <class 'list'>  <class 'str'>
2  <class 'int'>  <class 'list'>  <class 'str'>

a = (df.applymap(type) == list).all()
print (a)
X    False
Y     True
Z    False
dtype: bool

Or:

a = df.applymap(lambda x: isinstance(x, list)).all()
print (a)
X    False
Y     True
Z    False
dtype: bool

And if need list of columns:

L = a.index[a].tolist()
print (L)
['Y']

If want check dtypes (but strings, list, dict are objects):

print (df.dtypes)
X     int64
Y    object
Z    object
dtype: object

a = df.dtypes == 'int64'
print (a)
X     True
Y    False
Z    False
dtype: bool