diff --git a/wgmaster/migrate.py b/wgmaster/migrate.py
index cfd1613..aeb7acc 100755
--- a/wgmaster/migrate.py
+++ b/wgmaster/migrate.py
@@ -12,10 +12,10 @@ import requests
 
 DB_CNX: Optional[sqlite3.Connection] = None
 
-USTID_RE = re.compile('[A-Z]{2}[A-Z0-9]{2,12}')
-BIC_RE = re.compile('[A-Z0-9]{4}[A-Z]{2}[A-Z0-9]{2}([A-Z0-9]{3})?')
-IBAN_RE = re.compile('[A-Z]{2}[0-9]{2}[A-Z0-9]{8,30}')
-EMAIL_RE = re.compile('[^@\s]+@([a-z0-9_äöüß-]+\.)+[a-z]{2,}')
+USTID_RE = re.compile(r'[A-Z]{2}[A-Z0-9]{2,12}')
+BIC_RE = re.compile(r'[A-Z0-9]{4}[A-Z]{2}[A-Z0-9]{2}([A-Z0-9]{3})?')
+IBAN_RE = re.compile(r'[A-Z]{2}[0-9]{2}[A-Z0-9]{8,30}')
+EMAIL_RE = re.compile(r'[^@\s]+@([a-z0-9_äöüß-]+\.)+[a-z]{2,}')
 
 CULTIVATION_MAP: Optional[Dict[int, str]] = {1: 'N', 2: 'KIP', 3: 'BIO'}
 
@@ -61,10 +61,10 @@ STREET_NAMES: Dict[str, str] = {
 
 
 def parse_csv(filename: str) -> Iterator[Dict[str, Any]]:
-    def parse_line(l: str) -> Iterator[str]:
+    def parse_line(line_str: str) -> Iterator[str]:
         w = None
         s = False
-        for ch in l:
+        for ch in line_str:
             if w is None:
                 if ch == ';':
                     yield ''
@@ -103,7 +103,7 @@ def parse_csv(filename: str) -> Iterator[Dict[str, Any]]:
                     part = False
                 elif part.isdigit():
                     part = int(part)
-                elif re.match('[0-9]+\.[0-9]+', part):
+                elif re.match(r'[0-9]+\.[0-9]+', part):
                     part = float(part)
                 elif len(part) == 10 and part[4] == '-' and part[7] == '-':
                     part = datetime.datetime.strptime(part, '%Y-%m-%d').date()
@@ -113,17 +113,17 @@ def parse_csv(filename: str) -> Iterator[Dict[str, Any]]:
             yield obj
 
 
-def format_row(*args) -> str:
+def format_row(*values) -> str:
     row = ''
-    for arg in args:
-        if arg is None:
+    for val in values:
+        if val is None:
             pass
-        elif type(arg) == str:
-            row += f'"{arg}"'
-        elif type(arg) == bool:
-            row += 'T' if arg else 'F'
+        elif type(val) == str:
+            row += f'"{val}"'
+        elif type(val) == bool:
+            row += 'T' if val else 'F'
         else:
-            row += str(arg)
+            row += str(val)
         row += ';'
     return f'{row[:-1]}\n'
 
@@ -146,7 +146,8 @@ def convert(mgnr: int, key: str, old_value: str, new_value: str) -> None:
         print(f'\x1B[1m{mgnr:>6}: {key:<12} "{old_value}" -> "{new_value}"\x1B[0m', file=sys.stderr)
 
 
-def convert_name(mgnr: int, old_name: Tuple[str, str], new_name: Tuple[str, str, str, str, str], billing: Optional[str] = None) -> None:
+def convert_name(mgnr: int, old_name: Tuple[str, str], new_name: Tuple[str, str, str, str, str],
+                 billing: Optional[str] = None) -> None:
     if not args.quiet:
         print(f'\x1B[1m{mgnr:>6}: '
               f'{" / ".join([e or "" for e in old_name])} -> '
@@ -164,6 +165,7 @@ def check_lfbis_nr(nr: str) -> bool:
     v = (11 - (s % 11)) % 10
     return v == int(nr[-1])
 
+
 def check_ustid_at(nr: str) -> bool:
     # http://www.pruefziffernberechnung.de/U/USt-IdNr.shtml
     if not nr.startswith('ATU') or len(nr) != 11 or not nr[3:].isdigit():
@@ -175,26 +177,18 @@ def check_ustid_at(nr: str) -> bool:
     return v == int(nr[-1])
 
 
-def iban_checksum(iban: str) -> int:
-    if not IBAN_RE.fullmatch(iban):
-        raise RuntimeError()
-    s = re.sub('[A-Z]', lambda ch: str(ord(ch.group(0)) - ord('A') + 10), (iban[4:] + iban[:4]))
-    v = 98 - (int(s) % 97)
-    return v
+def modulo(a: str, b: int) -> int:
+    s = 0
+    for ch in a:
+        s = (s * 10 + int(ch)) % b
+    return s
 
 
 def check_iban(iban: str) -> bool:
     if not IBAN_RE.fullmatch(iban):
         return False
-    return iban_checksum(iban) == 97
-
-
-def generate_iban_at(blz: int, ktonr: str) -> str:
-    if blz > 99999 or len(ktonr) > 11:
-        raise RuntimeError()
-    iban = f'AT00{blz:>05}{ktonr:>011}'
-    s = iban_checksum(iban)
-    return iban.replace('00', f'{s:02}', 1)
+    s = re.sub('[A-Z]', lambda ch: str(ord(ch.group(0)) - ord('A') + 10), (iban[4:] + iban[:4]))
+    return modulo(s, 97) == 1
 
 
 def normalize_phone_nr(nr: str) -> str:
@@ -277,7 +271,10 @@ def lookup_gem_name(name: str) -> List[Tuple[int, int]]:
         name = 'Grub an der March'
 
     cur = DB_CNX.cursor()
-    cur.execute("SELECT k.kgnr, k.name, g.gkz, g.name FROM AT_kg k JOIN AT_gem g ON g.gkz = k.gkz JOIN wb_gem wg ON wg.gkz = g.gkz "
+    cur.execute("SELECT k.kgnr, k.name, g.gkz, g.name "
+                "FROM AT_kg k "
+                "JOIN AT_gem g ON g.gkz = k.gkz "
+                "JOIN wb_gem wg ON wg.gkz = g.gkz "
                 "WHERE LOWER(k.name) LIKE (LOWER(?) || '%') AND wg.hkid = 'WLWV'",
                 (name.replace('Gr.', 'Groß ').replace('Groß ', 'Groß').replace('-', ''),))
     rows: List[Tuple[int, str, int, str]] = cur.fetchall()
@@ -322,7 +319,7 @@ def migrate_reeds(in_dir: str, out_dir: str) -> None:
             if name.isupper():
                 name = name.title()
 
-            gem  = GEM_MAP[r['GNR']]
+            gem = GEM_MAP[r['GNR']]
             kgnr = gem[0][0]
             if len(gem) != 1:
                 print(gem, name, '->', gem[0])
@@ -336,7 +333,7 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
     members = parse_csv(f'{in_dir}/TMitglieder.csv')
     fbs = parse_flaechenbindungen(in_dir)
 
-    with open(f'{out_dir}/member.csv', 'w+') as f_m,open(f'{out_dir}/member_billing_address.csv', 'w+') as f_mba:
+    with open(f'{out_dir}/member.csv', 'w+') as f_m, open(f'{out_dir}/member_billing_address.csv', 'w+') as f_mba:
         f_m.write('mgnr;predecessor_mgnr;prefix;given_name;middle_names;family_name;suffix;'
                   'birthday;entry_date;exit_date;business_shares;accounting_nr;zwstid;'
                   'lfbis_nr;ustid;volllieferant;buchführend;funktionär;active;iban;bic;'
@@ -358,8 +355,8 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                 continue
 
             given_name = given_name or ''
-            family_name = re.sub('\s+', ' ', family_name).strip()
-            given_name = re.sub('\s+', ' ', given_name).strip().replace(', ', ',')
+            family_name = re.sub(r'\s+', ' ', family_name).strip()
+            given_name = re.sub(r'\s+', ' ', given_name).strip().replace(', ', ',')
 
             if ' ' in family_name or '.' in family_name or ',' in family_name:
                 if family_name.endswith(' KG'):
@@ -367,9 +364,10 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                     family_name = parts[0].title()
                     billing_name = f'{family_name} KG'
 
-                convert_name(mgnr, (m['Nachname'], m['Vorname']), (prefix, given_name, middle_names, family_name, suffix), billing_name)
+                convert_name(mgnr, (m['Nachname'], m['Vorname']),
+                             (prefix, given_name, middle_names, family_name, suffix), billing_name)
             elif (' ' in given_name or '.' in given_name or ',' in given_name) and given_name != 'EVA MARIA':
-                if ' u. '  in given_name.lower() or ' u ' in given_name.lower() or ' und ' in given_name.lower():
+                if ' u. ' in given_name.lower() or ' u ' in given_name.lower() or ' und ' in given_name.lower():
                     parts = given_name.split(' ')
                     family_name = family_name.title()
                     billing_name = f'{family_name} {parts[0].title()} und {parts[-1].title()}'
@@ -382,7 +380,8 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                     family_name = family_name.title()
                     given_name = given_name.split(' ')[0].title()
                     billing_name = f'{family_name} {given_name} KEG'
-                elif given_name.lower().endswith(' jun') or given_name.lower().endswith(' jun.') or given_name.lower().endswith(' sen') or given_name.lower().endswith(' sen.'):
+                elif given_name.lower().endswith(' jun') or given_name.lower().endswith(' jun.') or \
+                        given_name.lower().endswith(' sen') or given_name.lower().endswith(' sen.'):
                     family_name = family_name.title()
                     parts = given_name.split(' ')
                     suffix = parts[-1].lower()
@@ -398,7 +397,8 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                     family_name = family_name.title()
                     given_name = given_name.split(' ')[0].title()
                     prefix = 'Dipl.-Ing.'
-                elif given_name.lower().endswith(' ing') or given_name.lower().endswith(' ing.') or given_name.lower().endswith(' dr') or given_name.lower().endswith(' dr.'):
+                elif given_name.lower().endswith(' ing') or given_name.lower().endswith(' ing.') or \
+                        given_name.lower().endswith(' dr') or given_name.lower().endswith(' dr.'):
                     family_name = family_name.title()
                     parts = given_name.split(' ')
                     given_name = parts[0].title()
@@ -406,7 +406,8 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                     if prefix[-1] != '.':
                         prefix += '.'
 
-                convert_name(mgnr, (m['Nachname'], m['Vorname']), (prefix, given_name, middle_names, family_name, suffix), billing_name)
+                convert_name(mgnr, (m['Nachname'], m['Vorname']),
+                             (prefix, given_name, middle_names, family_name, suffix), billing_name)
             else:
                 family_name = family_name.title()
                 given_name = given_name.title()
@@ -425,7 +426,6 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                         invalid(mgnr, 'BetriebsNr.', bnr)
                     bnr = None
 
-
             ustid: Optional[str] = m['UID']
             if ustid is not None:
                 ustid = ustid.replace(' ', '')
@@ -444,7 +444,7 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
             iban: Optional[str] = m['IBAN']
             bic: Optional[str] = m['BIC']
             blz: Optional[int] = m['BLZ']
-            ktonr: Optional[str] = m['KontoNr']
+            kto_nr: Optional[str] = m['KontoNr']
 
             if iban is None:
                 pass
@@ -455,10 +455,6 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                     invalid(mgnr, 'IBAN', iban)
                     iban = None
 
-            if iban is None and blz and ktonr:
-                iban = generate_iban_at(blz, re.sub('[. -]', '', ktonr))
-                success(mgnr, 'IBAN', f'{iban} ({blz}, {ktonr})')
-
             if bic is not None:
                 bic = bic.upper()
                 if bic == 'RLNWATAUE':
@@ -474,7 +470,8 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
             address: Optional[str] = m['Straße']
             if address is not None:
                 address_old = address
-                address = re.sub('([0-9])([A-Z])', lambda a: a.group(1) + a.group(2).lower(), re.sub('\s+', ' ', address).strip().title())
+                address = re.sub('([0-9])([A-Z])', lambda a: a.group(1) + a.group(2).lower(),
+                                 re.sub(r'\s+', ' ', address).strip().title())
                 address = address.replace('strasse', 'straße').replace('strassse', 'straße')\
                     .replace('Strasse', 'Straße').replace('Str.', 'Straße')\
                     .replace('str.', 'straße').replace('ster.', 'straße').replace('g. ', 'gasse ')\
@@ -487,7 +484,8 @@ def migrate_members(in_dir: str, out_dir: str) -> None:
                 elif address.startswith('Ob. '):
                     address = address.replace('Ob. ', 'Obere ', 1)
                 address = address.replace(' Nr. ', ' ')
-                address = re.sub(r'([^0-9]+?)( [0-9])', lambda a: STREET_NAMES.get(a.group(1), a.group(1)) + a.group(2), address)
+                address = re.sub(r'([^0-9]+?)( [0-9])',
+                                 lambda a: STREET_NAMES.get(a.group(1), a.group(1)) + a.group(2), address)
                 if address_old != address:
                     convert(mgnr, 'Adresse', address_old, address)
 
@@ -594,8 +592,8 @@ def migrate_contracts(in_dir: str, out_dir: str) -> None:
             if t - f < 50:
                 return [
                     gst
-                    for i in range(f, t + 1)
-                    for p in [f'{b or ""}{i}']
+                    for counter in range(f, t + 1)
+                    for p in [f'{b or ""}{counter}']
                     for gst in parse_gstnrs(p, kgnr, mgnr)
                 ]