# otp.Source.add_prefix

#### Source.add_prefix(prefix, inplace=False, columns=None, ignore_columns=None)

Adds prefix to all column names (except **TIMESTAMP** (or **Time**) special column).

* **Parameters:**
  * **prefix** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) -- String prefix to add to all columns.
  * **inplace** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) -- The flag controls whether operation should be applied inplace or not.
    If `inplace=True`, then it returns nothing. Otherwise method returns a new modified
    object.
  * **columns** (*List* *[*[*str*](https://docs.python.org/3/library/stdtypes.html#str) *]* *,* *optional*) -- If set, only selected columns will be updated with prefix. Can't be used with `ignore_columns` parameter.
  * **ignore_columns** (*List* *[*[*str*](https://docs.python.org/3/library/stdtypes.html#str) *]* *,* *optional*) -- If set, selected columns won't be updated with prefix. Can't be used with `columns` parameter.
  * **self** ([*Source*](root.md#onetick.py.Source))
* **Return type:**
  [`Source`](root.md#onetick.py.Source) or `None`

### Examples

Add prefix *test_* to all columns (note that column **Time** is not renamed):

```pycon
>>> data = otp.DataSource(db='US_COMP', tick_type='TRD', symbols='AAPL')
>>> data = data.add_prefix('test_')
>>> otp.run(data, start=otp.dt(2022, 3, 1), end=otp.dt(2022, 3, 2))
                     Time  test_PRICE  test_SIZE
0 2022-03-01 00:00:00.000         1.3        100
1 2022-03-01 00:00:00.001         1.4         10
2 2022-03-01 00:00:00.002         1.4         50
```

Parameter `columns` specifies columns to be updated with prefix:

```pycon
>>> data = otp.Tick(A=1, B=2, C=3, D=4, E=5)
>>> data = data.add_prefix('test_', columns=['A', 'B', 'C'])
>>> otp.run(data)
        Time  test_A  test_B  test_C  D  E
0 2003-12-01       1       2       3  4  5
```

Parameter `ignore_columns` specifies columns to ignore:

```pycon
>>> data = otp.Tick(A=1, B=2, C=3, D=4, E=5)
>>> data = data.add_prefix('test_', ignore_columns=['A', 'B', 'C'])
>>> otp.run(data)
        Time  A  B  C  test_D  test_E
0 2003-12-01  1  2  3       4       5
```

Parameters `columns` and `ignore_columns` can't be used at the same time:

```pycon
>>> data = otp.Tick(A=1, B=2, C=3, D=4, E=5)
>>> data.add_prefix('test_', columns=['B', 'C'], ignore_columns=['A'])
Traceback (most recent call last):
    ...
ValueError: It is allowed to use only one of `columns` or `ignore_columns` parameters at a time
```

Columns can't be renamed if their resulting name will be equal to existing column name:

```pycon
>>> data = otp.Tick(X=1, XX=2)
>>> data.add_prefix('X', columns=['X'])
Traceback (most recent call last):
    ...
AttributeError: Column XX already exists, please, use another prefix
```