python - check if variable is dataframe

172
votes

when my function f is called with a variable I want to check if var is a pandas dataframe:

def f(var):
    if var == pd.DataFrame():
        print "do stuff"

I guess the solution might be quite simple but even with 

def f(var):
    if var.values != None:
        print "do stuff"

I can't get it to work like expected.

2
pythonpandas
Your code says "if var is equal to an empty dataframe". What you really want is "if the type of var is equal to the type pd.DataFrame". You can check that using isinstance - Katriel

2 Answers

243
votes

Use isinstance, nothing else:

if isinstance(x, pd.DataFrame):
    ... # do something

PEP8 says explicitly that isinstance is the preferred way to check types

No:  type(x) is pd.DataFrame
No:  type(x) == pd.DataFrame
Yes: isinstance(x, pd.DataFrame)

And don't even think about

if obj.__class__.__name__ = 'DataFrame':
    expect_problems_some_day()

isinstance handles inheritance (see What are the differences between type() and isinstance()?). For example, it will tell you if a variable is a string (either str or unicode), because they derive from basestring)

if isinstance(obj, basestring):
    i_am_string(obj)

Specifically for pandas DataFrame objects:

import pandas as pd
isinstance(var, pd.DataFrame)
135
votes

Use the built-in isinstance() function.

import pandas as pd

def f(var):
    if isinstance(var, pd.DataFrame):
        print("do stuff")