Convert a ROOT file to a JSON file when the structure is just a list of TTrees with PyROOT

Root2Json.py

import argparse
import json
import sys

from ROOT import TTree,TFile


def root_to_dict(in_file):
	root_fp = TFile(in_file)
	file_kl = root_fp.GetListOfKeys()
	
	rv = {}
	for key in file_kl:
		c_tree = root_fp.Get(key.GetName())
		if not isinstance(c_tree, TTree):
			continue
		
		tree_as_list = []
		# get leaves info
		leaf_info = [(tree_leaf.GetName(), tree_leaf.GetTypeName(), tree_leaf.GetLen(), tree_leaf) for tree_leaf in c_tree.GetListOfLeaves()]
		
		# Iterate through entires
		for entry_num in range(c_tree.GetEntries()):
			c_tree.GetEntry(entry_num)
			c_entry = {}
			
			# Iterate through leafs
			for leaf_name, leaf_type, n_vals, c_leaf in leaf_info:
				if leaf_type == "Char_t":
					c_entry[leaf_name] = [c_leaf.GetValueString(i) for i in range(n_vals)]
				elif leaf_type in ("Int_t", "ULong64_t", "UInt_t", "UShort_t"):
					c_entry[leaf_name] = [int(c_leaf.GetValue(i)) for i in range(n_vals)]
				elif leaf_type in ("Float_t", "Double_t"):
					c_entry[leaf_name] = [c_leaf.GetValue(i) for i in range(n_vals)]
				else:
					print("Unknown Type, Please Modify to accommodate ", leaf_type)
					print("Go to https://root.cern.ch/doc/master/classTLeaf.html#a06e8bfb89e1dc6e32ed1709eaaa814f1 then \
					select the specific TLeaf Type that holds this value to see if GetValue() or another function is best at parsing this particular Leaf Type")
					sys.exit(0)
			
			tree_as_list.append(c_entry)
		rv[c_tree.GetName()] = tree_as_list
	
	root_fp.Close()
	return rv


if __name__ == "__main__":
	parser = argparse.ArgumentParser(description="Convert a ROOT file to a JSON file")
	parser.add_argument('filename', help='input root filename')
	args = parser.parse_args()
	out_dict = root_to_dict(args.filename)
	with open(f"{args.filename.replace('.root','')}.json",'w') as fp:
		json.dump(out_dict, fp, indent=2)