# otp.Source.logf

#### Source.logf(message, severity, \*args, where=None, inplace=False)

Call built-in OneTick `LOGF` function.

* **Parameters:**
  * **message** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) -- Log message/format string. The underlying formatting engine is the Boost Format Library:
    [https://www.boost.org/doc/libs/1_53_0/libs/format/doc/format.html](https://www.boost.org/doc/libs/1_53_0/libs/format/doc/format.html)
  * **severity** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) -- Severity of message. Supported values: `ERROR`, `WARNING` and `INFO`.
  * **where** ([*Operation*](../operation/root.md#onetick.py.Operation)) -- A condition that allows to filter ticks to call `LOGF` on. `None` for no filtering.
  * **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.
  * **args** ([*list*](https://docs.python.org/3/library/stdtypes.html#list)) -- Parameters for format string (optional).
  * **self** ([*Source*](root.md#onetick.py.Source))
* **Return type:**
  [`Source`](root.md#onetick.py.Source)

### Examples

```pycon
>>> data = otp.Ticks(PRICE=[97, 99, 103])
>>> data = data.logf("PRICE (%1%) is higher than 100", "WARNING", data["PRICE"], where=(data["PRICE"] > 100))
```