Python: Eliminating rows in Pandas DataFrame based on boolean condition -

suppose have dataframe in pandas like

   c1   c2 0  'ab'  1 1  'ac'  0 2  'bd'  0 3  'fa'  1 4  'de'  0 

and want show rows such c1 doesn't contain 'a'. desired output be:

   c1   c2 2  'bd'  0 4  'de'  0 

my first attempt use df.loc, this:

df.loc['a' not in df['c1']] 

for searching specific values, df.loc works fine, searching based on false condition ('a' not in df['c1']) doesn't.

i know can reverse thing. mean, can return rows contain 'a' in column 'c1', through code:

df.loc[df['c1'].str.contains('a')] 

but can't figure out elegant/concise way other way around. how can that?

use ~ flip series of booleans:

df.loc[~df['c1'].str.contains('a')]