pythmpg.parse_jahn

Parser for index symmetrization information in Jahn symbols.

Defines two functions intended to be called externally: parse_jahn_symbol(), which parses Jahn symbols into structured instruction blocks describing the needed symmetrization or antisymmetrization over tensor axes, and jahn_rank() to return the rank of the tensor.

Notes

Jahn symbols passed to the parser should lack any preceding 'a' or 'e' characters. Results are cached in the module-level jahn_dict to avoid redundant parsing of repeated symbols.

exception pythmpg.parse_jahn.ParsingError

Bases: Exception

pythmpg.parse_jahn.find_match(text)

Find the closing bracket that matches the opening bracket at index 0.

Parameters:

text (str) – String whose first character is either '[' or '{'.

Returns:

ic – Index of the character immediately after the matching closing bracket (i.e., the length of the balanced sub-string).

Return type:

int

Raises:

ParsingError – If the string ends before a matching closing bracket is found.

pythmpg.parse_jahn.jahn_rank(instructions)

Determine the tensor rank from a parsed operation specification.

Parameters:

instructions (tuple) – Nested instruction specification as returned by parse_jahn_symbol().

Returns:

rank – Rank of the tensor (zero in the case of scalars).

Return type:

int

pythmpg.parse_jahn.list_to_tuple(job, b_text, depth)

Recursively parse a block text string into an instruction tuple

Constructs and returns an instruction block of the form (job, obj_list), where obj_list is a list of axes or sub-blocks, built by recursively processing any nested bracket groups found in b_text. The global axis counter is also incremented for each tensor axis encountered.

Parameters:

• job (str) – Symmetrization mode for this block: 'nosymm', 'symm', or 'asymm'.

• b_text (str) – Block text string to be parsed, e.g., '1[22]1'.

• depth (int) – Current recursion depth, used for indented debug printing and as a guard against runaway recursion.

Returns:

result – Parsed instruction block in the form of a tuple (job, obj_list), or the unwrapped inner tuple when the block reduces to a single sub-tuple under 'nosymm'.

Return type:

tuple

Raises:

ParsingError – If b_text contains elements of inconsistent type under a symmetrizing job, an empty list is found, fewer than two sub-blocks appear where multiple are required, or an unexpected object type is encountered.

pythmpg.parse_jahn.parse_jahn_symbol(jahn, if_print=False)

Parse the index symmetrization information in a Jahn symbol.

Converts the Jahn symbol into an instruction set represented as a nested tuple structure specifying which tensor axes are subject to symmetrization or antisymmetrization. Results are cached in jahn_dict so that repeated calls with the same symbol entail no overhead.

Parameters:

• jahn (str) – Jahn symbol to parse, lacking any preceding 'a' or 'e' characters.

• if_print (bool, optional) – If True, print intermediate parsing steps to stdout. Default is False.

Returns:

instructions – Nested tuple specifying tensor axes and the symmetrization operations to be applied to them. Returns None if the symbol contains illegal characters or if the parser fails.

Return type:

tuple or None

pythmpg.parse_jahn.parse_string(b_string)

Tokenise a block text string into a mixed list of ints and strings.

Parameters:

b_string (str) – String in Jahn block-text format, e.g., '1[{2}{2}]2'.

Returns:

b_list – Mixed list of integers (single-digit axis counts) and strings (bracketed sub-blocks), e.g., [1, '[{2}{2}]', 2].

Return type:

list

Raises:

ParsingError – If an unexpected character is encountered in b_string.