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Parse Molcas/OpenMolcas log files in a modular way

Project description


A rule-based parser for Molcas/OpenMolcas log files to extract and transform any data found in a log file.

Molextract provides a more modular approach to extracting information from log files and abstracts out similar control flow seen in many scripts. The initial motivation to develop molextract came from wanting to centralize multiple bash scripts that used grep, awk and sed into one Python API.

Molextract is abstract enough that it really isn't specific to Molcas/OpenMolcas log files. Any file that has certain start / end markers would be suitable to use the same infrastructure.

High Level Overview

Some information is easily extracted from OpenMolcas log files. For example the Total SCF energy in the log file is always printed prefixed as :: Total SCF energy <energy>. Other information is prefixed by various different "tags" or markers of this information.

The goal of molextract is to create a standard and modular way to extract this information so as to avoid many scripts that extract different information each in slightly different ways.

Furthermore, molextract is designed to simply extract information, so that any application can modify / change / transform this data in any way fit.


The design of molextract is meant to mimic that of Lex, a lexical analyzer. So, molextract is built to allow lexing to be easy for the user, but all the parsing or giving meaning to the data is all on the user.

A core concept in Lex is that of "Rules". A Rule is simply something that associates a regular expression with some code to execute.

Back to the SCF example before, we could make a Rule that matches the RegEx :: Total SCF energy. Once that rule matches that line in the Python code we now have access to the String ":: Total SCF energy <energy>" and then we can do... anything. Most likely we want the energy as a float so we can do something like energy = float(line.split()[4]). In this example we can say this Rule's start_tag is the RegEx :: Total SCF energy.

Sometimes data in OpenMolcas log files span multiple lines so our start_tag may be on line 1, but all our data is on lines 2-10. So we also need a mechanism to know when a rule no longer applies or an end_tag. This is yet another RegEx that once we match a start_tag is constantly checked to see if our Rule is complete.

Let's see this high level overview in some of the code. Ignore the method names for now and focus on the START_TAG and END_TAG class variables. This is the RASSCFOrbSpec rule found here. It's goal is the take the following information

++    Orbital specifications:
      Symmetry species                           1
      Frozen orbitals                            0
      Inactive orbitals                         27
      Active orbitals                           10
      RAS1 orbitals                              0
      RAS2 orbitals                             10
      RAS3 orbitals                              0
      Secondary orbitals                       148
      Deleted orbitals                           0
      Number of basis functions                185

and convert it to the following Python dictionary

    "active_orbs": 10,
    "num_basis_funcs": 185

The code for to that looks like this

class RASSCFOrbSpec(Rule):
    START_TAG = r"\+\+    Orbital specifications:"
    END_TAG = "--"

    def __init__(self):
        super().__init__(self.START_TAG, self.END_TAG)
        self.state = {"active_orbs": None, "num_basis_funcs": None}

    def process_lines(self, start_line):
        # Don't care about next two lines
        for line in self:
            last = line.split()[-1]
            if "Active orbitals" in line:
                self.state["active_orbs"] = int(last)
            elif "Number of basis functions" in line:
                self.state["num_basis_funcs"] = int(last)

    def reset(self):
        tmp = self.state.copy()
        self.state = {"active_orbs": None, "num_basis_funcs": None}
        return tmp

First notice how the data itself has very obvious start / end tags. Namely the data starts with ++ Orbital specifications: and ends with --. These are then precisely our RegExs we define for our Rule, see the START_TAG and END_TAG variables.

The process_lines method will handle the actual extraction of data. See the Parse section to understand when and where this method is executed. For now you can assume that process_lines is only called when we are reading a log file and we find a line that matches START_TAG.

Once process_lines is called we are given access to the line that matches the START_TAG namely the argument start_line. We are now also able to iterate through the rest of the log file until we see a line that matches the END_TAG. This iteration is encapsulated in the python code for line in self, i.e. the for loop will end once we reach a line matching END_TAG. Based on these control flows, within the for loop we know exactly where we are in the log file and are free to parse as we please. In our case we want some specific number so we write some standard python string manipulation code.

The reset method is a mechanism to allow the re-use of a Rule between multiple files as there may be some state that needs to be reset. Understanding this mechanism is ancillary to the core concept of Rules in molextract.

This was a simple rule. molextract allows us to nest rules so we can build complex rules that describe an entire module or an entire calculation. See examples/ and try to follow the chain as described below.

- LogRule
  > RASSCFModule
    * RASSCFEnergy
    * RASSCFCiCoeff
    * RASSCFOccupation
    * RASSCFOrbSpec
    * RASSCFCIExpansionSpec
  > MCPDFTModule
    * MCPDFTRefEnergy
    * MCPDFTEnergy
  > RASSIModule
    * RASSIDipoleStrengths


In the Rules section we made some assumptions about when and where process_lines is called. The Parser class explicitly defines these mechanism.

In the Parser class we have a method feed

    def feed(self, data, delim='\n'):
        split = data.split(delim)
        split_iter = iter(split)

        for line in split_iter:
            if self.rule.start_tag_matches(line):
                return self.rule.reset()

We do the following in this method

  1. Setup the internal iterator for the rule by splitting the data
  2. Iterate through the same iterator and only when we find the line that matches start_tag do we execute process_lines
  3. Once the rule is finished executing we immediately return with the data as returned in reset

Here we have explicitly defined when and where to call process_lines. It is up to the user to manage when and where to execute this method, but the Parser class should suffice for almost all use cases.


Manual Installation

molextract has no external dependencies. You can simply clone this repository and add that location to your $PYTHONPATH

For example if you want to put this in /home/$USER/python-packages do the following.

mkdir -p /home/$USER/python-packages
cd /home/$USER/python-packages
git clone

Then in your ~/.bashrc or other runtime configuration file, add the following line

export PYTHONPATH=$PYTHONPATH:/home/$USER/python-packages/molextract

Local pip install

You may also install molextract locally via setuptools. Clone the repository and run within it

pip install .

Remote pip install

Currently this package is not yet available on pypi


See the examples/ directory. You can run these scripts with the files found in the test/test_files directory.


To run the unit tests you will need pytest installed in your current python environment. Then simply run pytest within this repository.

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