Add Python example export_account_totals.py

This example exports acount totals of all accounts into a CSV file.

This has been asked before: https://money.stackexchange.com/questions/111786/exporting-account-totals-in-gnucash

bindings/python/example_scripts/CMakeLists.txt

@@ -2,6 +2,7 @@
 set(example_scripts_DATA
         account_analysis.py
         change_tax_code.py
+        export_account_totals.py
         Invoice.tex
         latex_invoices.py
         new_book_with_opening_balances.py

bindings/python/example_scripts/export_account_totals.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+
+# export_account_totals -- export the account totals of all accounts.
+
+# Copyright (C) 2020 Hong Xu <hong@topbug.net>
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation; either version 2 of
+# the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# @author Hong Xu <hong@topbug.net>
+
+# Usage:
+#
+#    python3 export_account_totals.py /path/to/gnucash_book_file > output.csv
+
+import copy
+import sys
+
+from gnucash import GncNumeric, Session, SessionOpenMode
+
+
+def get_all_sub_accounts(account, names=[]):
+    "Iterate over all sub accounts of a given account."
+
+    for child in account.get_children_sorted():
+        child_names = names.copy()
+        child_names.append(child.GetName())
+        yield child, '::'.join(child_names)
+        yield from get_all_sub_accounts(child, child_names)
+
+
+def to_string_with_decimal_point_placed(number: GncNumeric):
+    """Convert a GncNumeric to a string with decimal point placed if permissible.
+    Otherwise returns its fractional representation.
+    """
+
+    number = copy.copy(number)
+    if not number.to_decimal(None):
+        return str(number)
+
+    nominator = str(number.num())
+    point_place = str(number.denom()).count('0')  # How many zeros in the denominator?
+    if point_place == 0:
+        return nominator
+
+    if len(nominator) <= point_place:  # prepending zeros if the nominator is too short
+        nominator = '0' * (point_place - len(nominator)) + nominator
+
+    return '.'.join([nominator[:-point_place - 1], nominator[-point_place:]])
+
+
+if __name__ == '__main__':
+    print('Name,Commodity,Totals,Totals (USD)')
+    with Session(sys.argv[1], SessionOpenMode.SESSION_READ_ONLY) as session:
+        commodity_table = session.book.get_table()
+        USD = commodity_table.lookup("ISO4217", "USD")
+        root_account = session.book.get_root_account()
+        for account, account_name in get_all_sub_accounts(root_account):
+            print(','.join([account_name,
+                            account.GetCommodity().get_mnemonic(),
+                            to_string_with_decimal_point_placed(account.GetBalance()),
+                            to_string_with_decimal_point_placed(account.GetBalanceInCurrency(USD, True))
+                            ]))