python - How to delete all columns in DataFrame except certain ones?

Question

Let's say I have a DataFrame that looks like this:

a  b  c  d  e  f  g  
1  2  3  4  5  6  7
4  3  7  1  6  9  4
8  9  0  2  4  2  1

How would I go about deleting every column besides a and b?

This would result in:

a  b
1  2
4  3
8  9

I would like a way to delete these using a simple line of code that says, delete all columns besides a and b, because let's say hypothetically I have 1000 columns of data.

Thank you.

Answer 1

In [48]: df.drop(df.columns.difference(['a','b']), 1, inplace=True)
Out[48]:
   a  b
0  1  2
1  4  3
2  8  9

or:

In [55]: df = df.loc[:, df.columns.intersection(['a','b'])]

In [56]: df
Out[56]:
   a  b
0  1  2
1  4  3
2  8  9

PS please be aware that the most idiomatic Pandas way to do that was already proposed by @Wen:

df = df[['a','b']]

or

df = df.loc[:, ['a','b']]