How to add a suffix (or prefix) to each column name?

The following is the nicest way to add suffix in my opinion.

df = df.add_suffix('_some_suffix')

As it is a function that is called on DataFrame and returns DataFrame - you can use it in chain of the calls.

You can use a list comprehension:

df.columns = [str(col) + '_x' for col in df.columns]

There are also built-in methods like .add_suffix() and .add_prefix() as mentioned in another answer.

Elegant In-place Concatenation

If you're trying to modify df in-place, then the cheapest (and simplest) option is in-place addition directly on df.columns (i.e., using Index.__iadd__).

df = pd.DataFrame({"A": [9, 4, 2, 1], "B": [12, 7, 5, 4]})
df

   A   B
0  9  12
1  4   7
2  2   5
3  1   4

df.columns += '_some_suffix'
df

   A_some_suffix  B_some_suffix
0              9             12
1              4              7
2              2              5
3              1              4

To add a prefix, you would similarly use

df.columns = 'some_prefix_' + df.columns
df

   some_prefix_A  some_prefix_B
0              9             12
1              4              7
2              2              5
3              1              4

Another cheap option is using a list comprehension with f-string formatting (available on python3.6+).

df.columns = [f'{c}_some_suffix' for c in df]
df

   A_some_suffix  B_some_suffix
0              9             12
1              4              7
2              2              5
3              1              4

And for prefix, similarly,

df.columns = [f'some_prefix{c}' for c in df]

Method Chaining

It is also possible to do add *fixes while method chaining. To add a suffix, use DataFrame.add_suffix

df.add_suffix('_some_suffix')

   A_some_suffix  B_some_suffix
0              9             12
1              4              7
2              2              5
3              1              4

This returns a copy of the data. IOW, df is not modified.

Adding prefixes is also done with DataFrame.add_prefix.

df.add_prefix('some_prefix_')

   some_prefix_A  some_prefix_B
0              9             12
1              4              7
2              2              5
3              1              4

Which also does not modify df.

Critique of add_*fix

These are good methods if you're trying to perform method chaining:

df.some_method1().some_method2().add_*fix(...)

However, add_prefix (and add_suffix) creates a copy of the entire dataframe, just to modify the headers. If you believe this is wasteful, but still want to chain, you can call pipe:

def add_suffix(df):
    df.columns += '_some_suffix'
    return df

df.some_method1().some_method2().pipe(add_suffix)

I haven't seen this solution proposed above so adding this to the list:

df.columns += '_x'

And you can easily adapt for the prefix scenario.

I Know 4 ways to add a suffix (or prefix) to your column's names:

1- df.columns = [str(col) + '_some_suffix' for col in df.columns]

or

2- df.rename(columns= lambda col: col+'_some_suffix')

or

3- df.columns += '_some_suffix' much easiar.

or, the nicest:

3- df.add_suffix('_some_suffix')