pseudonymise

The pseudonymisation rule for the header of an EDF or EDF+ recording.

The rule rewrites three fields of the 256-byte fixed header and copies every other byte, so a file keeps its length, its signals and its time of day:

Bytes	Field	Becomes
8–87	local patient identification	X X X X
88–167	local recording identification	Startdate D X X X
168–175	start date	01.01.85 if dates are removed

Every field is padded with spaces to its width. D is the header's own start date subfield, written dd-MMM-yyyy, when dates are kept and that subfield is a valid date; otherwise it is X. With dates kept, the start date field is copied; with dates removed, it becomes 01.01.85, EDF+'s marker for an unknown date.

The rule is strict and small:

• The header must be 256 bytes with version 0; anything else is refused.
• D is kept only when the recording field's first subfield is exactly Startdate and the second is a real calendar date in the form dd-MMM-yyyy. The month is read in any case and written in upper case, as EDF+ requires. Any other recording field, including the free text of a plain EDF file, gives D = X; a kept date then stays in the start date field alone.
• Bytes outside printable ASCII are not refused: the fields the rule writes are replaced whole, and every other byte is copied unchanged.
• Applying the rule twice gives the same bytes as applying it once.

The cases in pseudonymisation_vectors.json, shipped beside this module, fix the rule's output for any implementation of it.

PSEUDONYMOUS_PATIENT = 'X X X X' module-attribute

The local patient identification after the rule: every EDF+ subfield unknown.

REMOVED_START_DATE = '01.01.85' module-attribute

The start date field after the rule, when dates are removed.

is_pseudonymised(fixed_header, *, keep_dates)

Whether an EDF fixed header already follows the pseudonymisation rule.

Parameters:

Name	Type	Description	Default
fixed_header	bytes	The first 256 bytes of an EDF or EDF+ file.	required
keep_dates	bool	Whether the rule keeps the start date.	required

Returns:

Type	Description
bool	True if applying the rule would change nothing.

Raises:

Type	Description
ValueError	If fixed_header is not the fixed header of an EDF file.

pseudonymise_file_header(path, *, keep_dates)

Apply the pseudonymisation rule to the header of an EDF file, in place.

Only the first 256 bytes are read, and they are written back only if the rule changes them.

Parameters:

Name	Type	Description	Default
path	Path	The EDF or EDF+ file.	required
keep_dates	bool	Keep the start date, or replace it with EDF+'s marker for an unknown date.	required

Returns:

Type	Description
bool	True if the header was changed.

Raises:

Type	Description
ValueError	If the file does not start with the fixed header of an EDF file.

pseudonymise_header(fixed_header, *, keep_dates)

Apply the pseudonymisation rule to an EDF fixed header.

Parameters:

Name	Type	Description	Default
fixed_header	bytes	The first 256 bytes of an EDF or EDF+ file.	required
keep_dates	bool	Keep the start date, or replace it with EDF+'s marker for an unknown date.	required

Returns:

Type	Description
bytes	The rewritten 256 bytes.

Raises:

Type	Description
ValueError	If fixed_header is not the 256-byte fixed header of an EDF file with version 0.