diff --git a/analysis.py b/analysis.py
index d6e3518..6e2b9c8 100644
--- a/analysis.py
+++ b/analysis.py
@@ -1,3 +1,11 @@
+"""
+analysis
+========
+
+Library code for analysing captures returned by `Scope.capture()`.
+"""
+
+# pylama:ignore=C0103,R1716
 
 import numpy as np
 
@@ -62,7 +70,7 @@ def extract_waveform(series, period):
     p = int(round(series.sample_rate * period))
     n = len(series.samples) // p
     if n <= 2:
-        return None, None
+        return None, None, None, None
     samples = np.array(series.samples)[:p*n]
     cumsum = samples.cumsum()
     underlying = (cumsum[p:] - cumsum[:-p]) / p
@@ -94,7 +102,7 @@ def normalize_waveform(samples, smooth=7):
                 crossings.append((i - last_rising, last_rising))
     if first_falling is not None:
         crossings.append((n + first_falling - last_rising, last_rising))
-    width, first = min(crossings)
+    first = min(crossings)[1]
     wave = (np.hstack([samples[first:], samples[:first]]) - offset) / scale
     return wave, offset, scale, first, sorted((i - first % n, w) for (w, i) in crossings)
 
@@ -104,7 +112,7 @@ def characterize_waveform(samples, crossings):
     possibles = []
     if len(crossings) == 1:
         duty_cycle = crossings[0][1] / n
-        if duty_cycle > 0.45 and duty_cycle < 0.55:
+        if 0.45 < duty_cycle < 0.55:
             possibles.append((rms(samples - sine_wave(n)), 'sine', None))
             possibles.append((rms(samples - triangle_wave(n)), 'triangle', None))
             possibles.append((rms(samples - sawtooth_wave(n)), 'sawtooth', None))
diff --git a/scope.py b/scope.py
index e6848bf..2cd4b9e 100755
--- a/scope.py
+++ b/scope.py
@@ -1,4 +1,13 @@
-#!/usr/bin/env python3
+"""
+scope
+=====
+
+Code for talking to the BitScope series of USB digital mixed-signal scopes.
+Only supports the BS000501 at the moment, but that's only because it's never
+been tested on any other model.
+"""
+
+# pylama:ignore=E0611,E1101,W0201,W1203,W0631,C0103,R0902,R0912,R0913,R0914,R0915,C0415,W0601,W0102
 
 import argparse
 import array
@@ -178,23 +187,23 @@ class Scope(vm.VirtualMachine):
                 else:
                     Log.debug("- mode too slow")
                     continue
-                n = int(round(period / self.master_clock_period / ticks / clock_scale))
+                actual_nsamples = int(round(period / self.master_clock_period / ticks / clock_scale))
                 if len(analog_channels) == 2:
-                    n -= n % 2
+                    actual_nsamples -= actual_nsamples % 2
                 buffer_width = self.capture_buffer_size // capture_mode.sample_width
                 if logic_channels and analog_channels:
                     buffer_width //= 2
-                if n <= buffer_width:
-                    Log.debug(f"- OK; period is {n} samples")
-                    nsamples = n
+                if actual_nsamples <= buffer_width:
+                    Log.debug(f"- OK; period is {actual_nsamples} samples")
+                    nsamples = actual_nsamples
                     break
-                Log.debug(f"- insufficient buffer space for necessary {n} samples")
+                Log.debug(f"- insufficient buffer space for necessary {actual_nsamples} samples")
         else:
             raise ConfigurationError("Unable to find appropriate capture mode")
         sample_period = ticks*clock_scale*self.master_clock_period
         sample_rate = 1/sample_period
         if trigger_position and sample_rate > 5e6:
-            Log.warn("Pre-trigger capture not supported above 5M samples/s; forcing trigger_position=0")
+            Log.warning("Pre-trigger capture not supported above 5M samples/s; forcing trigger_position=0")
             trigger_position = 0
 
         if raw:
@@ -225,7 +234,7 @@ class Scope(vm.VirtualMachine):
         if trigger_level is None:
             trigger_level = (high + low) / 2
         analog_trigger_level = (trigger_level - analog_params.offset) / analog_params.scale if not raw else trigger_level
-        if trigger == 'A' or trigger == 'B':
+        if trigger in {'A', 'B'}:
             if trigger == 'A':
                 spock_option |= vm.SpockOption.TriggerSourceA
                 trigger_logic = 0x80
@@ -239,7 +248,7 @@ class Scope(vm.VirtualMachine):
             for channel, value in trigger.items():
                 if isinstance(channel, str):
                     if channel.startswith('L'):
-                        channel = int(channel[1:])
+                        channel = int(channel[1:])  # noqa
                     else:
                         raise ValueError("Unrecognised trigger value")
                 if channel < 0 or channel > 7:
@@ -268,8 +277,7 @@ class Scope(vm.VirtualMachine):
             if trigger_timeout > vm.Registers.Timeout.maximum_value:
                 if timeout > 0:
                     raise ConfigurationError("Required trigger timeout too long")
-                else:
-                    raise ConfigurationError("Required trigger timeout too long, use a later trigger position")
+                raise ConfigurationError("Required trigger timeout too long, use a later trigger position")
 
         Log.info(f"Begin {('mixed' if logic_channels else 'analogue') if analog_channels else 'logic'} signal capture "
                  f"at {sample_rate:,.0f} samples per second (trace mode {capture_mode.trace_mode.name})")
@@ -372,7 +380,7 @@ class Scope(vm.VirtualMachine):
                 Log.debug(f"Exact solution: size={size} nwaves={nwaves} clock={clock}")
                 break
             error = abs(frequency - actualf) / frequency
-            if error < max_error and (best_solution is None or error < best_solution[0]):
+            if error < max_error and (best_solution is None or error < best_solution[0]):  # noqa
                 best_solution = error, size, nwaves, clock, actualf
         else:
             if best_solution is None:
@@ -495,11 +503,11 @@ class Scope(vm.VirtualMachine):
         for lo in np.linspace(self.analog_lo_min, 0.5, n, endpoint=False):
             for hi in np.linspace(self.analog_hi_max, 0.5, n):
                 zero, full, offset = await measure(lo, hi, 2e-3 if len(items) % 4 < 2 else 1e-3, len(items) % 2 == 0)
-                if zero > 0.01 and full < 0.99 and full > zero:
+                if 0.01 < zero < full < 0.99:
                     analog_range = self.clock_voltage / (full - zero)
                     items.append((lo, hi, -zero*analog_range, (1-zero)*analog_range, offset*analog_range))
         await self.stop_clock()
-        lo, hi, low, high, offset = np.array(items).T
+        lo, hi, low, high, offset = np.array(items).T  # noqa
 
         def f(params):
             dl, dh = self.calculate_lo_hi(low, high, self.AnalogParams(*params, analog_scale, analog_offset, None, None, None))
@@ -514,7 +522,7 @@ class Scope(vm.VirtualMachine):
             Log.info(f"Calibration succeeded: {result.message}")
             params = self.AnalogParams(*result.x, analog_scale, analog_offset, None, None, None)
 
-            def f(x):
+            def f(x):  # noqa
                 lo, hi = self.calculate_lo_hi(x[0], x[1], params)
                 return np.sqrt((self.analog_lo_min - lo)**2 + (self.analog_hi_max - hi)**2)
 
@@ -536,23 +544,21 @@ class Scope(vm.VirtualMachine):
         return f"<Scope {self.url}>"
 
 
-"""
-$ ipython3 --pylab
-Using matplotlib backend: MacOSX
-
-In [1]: run scope
-
-In [2]: start_waveform(2000, 'triangle')
-Out[2]: 2000.0
-
-In [3]: traces = capture(['A','B'], period=1e-3, low=0, high=3.3)
-
-In [4]: plot(traces.A.timestamps, traces.A.samples)
-Out[4]: [<matplotlib.lines.Line2D at 0x10c782160>]
-
-In [5]: plot(traces.B.timestamps, traces.B.samples)
-Out[5]: [<matplotlib.lines.Line2D at 0x10e6ea320>]
-"""
+# $ ipython3 --pylab
+# Using matplotlib backend: MacOSX
+#
+# In [1]: run scope
+#
+# In [2]: start_waveform(2000, 'triangle')
+# Out[2]: 2000.0
+#
+# In [3]: traces = capture(['A','B'], period=1e-3, low=0, high=3.3)
+#
+# In [4]: plot(traces.A.timestamps, traces.A.samples)
+# Out[4]: [<matplotlib.lines.Line2D at 0x10c782160>]
+#
+# In [5]: plot(traces.B.timestamps, traces.B.samples)
+# Out[5]: [<matplotlib.lines.Line2D at 0x10e6ea320>]
 
 
 async def main():
diff --git a/streams.py b/streams.py
index 5f13b8f..d450a20 100644
--- a/streams.py
+++ b/streams.py
@@ -5,6 +5,8 @@ streams
 Package for asynchronous serial IO.
 """
 
+# pylama:ignore=W1203,R0916,W0703
+
 import asyncio
 import logging
 import sys
@@ -20,14 +22,14 @@ Log = logging.getLogger(__name__)
 class SerialStream:
 
     @classmethod
-    def devices_matching(cls, vid=None, pid=None, serial=None):
+    def devices_matching(cls, vid=None, pid=None, serial_number=None):
         for port in comports():
-            if (vid is None or vid == port.vid) and (pid is None or pid == port.pid) and (serial is None or serial == port.serial_number):
+            if (vid is None or vid == port.vid) and (pid is None or pid == port.pid) and (serial is None or serial_number == port.serial_number):
                 yield port.device
 
     @classmethod
-    def stream_matching(cls, vid=None, pid=None, serial=None, **kwargs):
-        for device in cls.devices_matching(vid, pid, serial):
+    def stream_matching(cls, vid=None, pid=None, serial_number=None, **kwargs):
+        for device in cls.devices_matching(vid, pid, serial_number):
             return SerialStream(device, **kwargs)
         raise RuntimeError("No matching serial device")
 
@@ -59,15 +61,15 @@ class SerialStream:
             return
         if not self._output_buffer:
             try:
-                n = self._connection.write(data)
+                nbytes = self._connection.write(data)
             except serial.SerialTimeoutException:
-                n = 0
+                nbytes = 0
             except Exception:
                 Log.exception("Error writing to stream")
                 raise
-            if n:
-                Log.debug(f"Write {data[:n]!r}")
-            self._output_buffer = data[n:]
+            if nbytes:
+                Log.debug(f"Write {data[:nbytes]!r}")
+            self._output_buffer = data[nbytes:]
         else:
             self._output_buffer += data
         if self._output_buffer and self._output_buffer_empty is None:
@@ -80,16 +82,16 @@ class SerialStream:
 
     def _feed_data(self):
         try:
-            n = self._connection.write(self._output_buffer)
+            nbytes = self._connection.write(self._output_buffer)
         except serial.SerialTimeoutException:
-            n = 0
-        except Exception as e:
+            nbytes = 0
+        except Exception as exc:
             Log.exception("Error writing to stream")
-            self._output_buffer_empty.set_exception(e)
+            self._output_buffer_empty.set_exception(exc)
             self._loop.remove_writer(self._connection)
-        if n:
-            Log.debug(f"Write {self._output_buffer[:n]!r}")
-            self._output_buffer = self._output_buffer[n:]
+        if nbytes:
+            Log.debug(f"Write {self._output_buffer[:nbytes]!r}")
+            self._output_buffer = self._output_buffer[nbytes:]
         if not self._output_buffer:
             self._loop.remove_writer(self._connection)
             self._output_buffer_empty.set_result(None)
@@ -101,40 +103,39 @@ class SerialStream:
                 data = bytes(self._output_buffer)
                 self._output_buffer_lock.release()
                 try:
-                    n = self._connection.write(data)
+                    nbytes = self._connection.write(data)
                 finally:
                     self._output_buffer_lock.acquire()
-                Log.debug(f"Write {self._output_buffer[:n]!r}")
-                self._output_buffer = self._output_buffer[n:]
+                Log.debug(f"Write {self._output_buffer[:nbytes]!r}")
+                self._output_buffer = self._output_buffer[nbytes:]
             self._output_buffer_empty = None
 
-    async def read(self, n=None):
+    async def read(self, nbytes=None):
         if self._use_threads:
-            return await self._loop.run_in_executor(None, self._read_blocking, n)
+            return await self._loop.run_in_executor(None, self._read_blocking, nbytes)
         while True:
-            w = self._connection.in_waiting
-            if w:
-                data = self._connection.read(w if n is None else min(n, w))
+            nwaiting = self._connection.in_waiting
+            if nwaiting:
+                data = self._connection.read(nwaiting if nbytes is None else min(nbytes, nwaiting))
                 Log.debug(f"Read {data!r}")
                 return data
-            else:
-                future = self._loop.create_future()
-                self._loop.add_reader(self._connection, future.set_result, None)
-                try:
-                    await future
-                finally:
-                    self._loop.remove_reader(self._connection)
+            future = self._loop.create_future()
+            self._loop.add_reader(self._connection, future.set_result, None)
+            try:
+                await future
+            finally:
+                self._loop.remove_reader(self._connection)
 
-    def _read_blocking(self, n=None):
+    def _read_blocking(self, nbytes=None):
         data = self._connection.read(1)
-        w = self._connection.in_waiting
-        if w and (n is None or n > 1):
-            data += self._connection.read(w if n is None else min(n-1, w))
+        nwaiting = self._connection.in_waiting
+        if nwaiting and (nbytes is None or nbytes > 1):
+            data += self._connection.read(nwaiting if nbytes is None else min(nbytes-1, nwaiting))
         Log.debug(f"Read {data!r}")
         return data
 
-    async def readexactly(self, n):
+    async def readexactly(self, nbytes):
         data = b''
-        while len(data) < n:
-            data += await self.read(n-len(data))
+        while len(data) < nbytes:
+            data += await self.read(nbytes-len(data))
         return data
diff --git a/utils.py b/utils.py
index cfd6e97..948717b 100644
--- a/utils.py
+++ b/utils.py
@@ -1,3 +1,9 @@
+"""
+utils
+=====
+
+Random utility classes/functions.
+"""
 
 
 class DotDict(dict):
diff --git a/vm.py b/vm.py
index d716a72..a2688ce 100644
--- a/vm.py
+++ b/vm.py
@@ -1,4 +1,3 @@
-
 """
 vm
 ==
@@ -13,6 +12,8 @@ document][VM01B].
 
 """
 
+# pylama:ignore=E221,C0326,R0904,W1203
+
 import array
 from collections import namedtuple
 from enum import IntEnum
@@ -35,30 +36,30 @@ class Register(namedtuple('Register', ['base', 'dtype', 'description'])):
         else:
             width = int(self.dtype[1:])
         if sign == 'U':
-            n = 1 << width
-            value = max(0, min(value, n-1))
-            bs = struct.pack('<I', value)
+            max_value = (1 << width) - 1
+            value = min(max(0, value), max_value)
+            data = struct.pack('<I', value)
         elif sign == 'S':
-            n = 1 << (width - 1)
-            value = max(-n, min(value, n-1))
-            bs = struct.pack('<i', value)
+            max_value = (1 << (width - 1))
+            value = min(max(-max_value, value), max_value - 1)
+            data = struct.pack('<i', value)
         else:
             raise TypeError("Unrecognised dtype")
-        return bs[:width//8]
+        return data[:width//8]
 
-    def decode(self, bs):
-        if len(bs) < 4:
-            bs = bs + bytes(4 - len(bs))
+    def decode(self, data):
+        if len(data) < 4:
+            data = data + bytes(4 - len(data))
         sign = self.dtype[0]
         if sign == 'U':
-            value = struct.unpack('<I', bs)[0]
+            value = struct.unpack('<I', data)[0]
         elif sign == 'S':
-            value = struct.unpack('<i', bs)[0]
+            value = struct.unpack('<i', data)[0]
         else:
             raise TypeError("Unrecognised dtype")
         if '.' in self.dtype:
-            whole, fraction = map(int, self.dtype[1:].split('.', 1))
-            value = value / (1 << fraction)
+            fraction = int(self.dtype.split('.', 1)[1])
+            value /= (1 << fraction)
         return value
 
     @property
@@ -69,15 +70,14 @@ class Register(namedtuple('Register', ['base', 'dtype', 'description'])):
             whole, fraction = int(self.dtype[1:]), 0
         if self.dtype[0] == 'S':
             whole -= 1
-        n = (1 << (whole+fraction)) - 1
-        return n / (1 << fraction) if fraction else n
+        max_value = (1 << (whole+fraction)) - 1
+        return max_value / (1 << fraction) if fraction else max_value
 
     @property
     def width(self):
         if '.' in self.dtype:
             return sum(map(int, self.dtype[1:].split('.', 1))) // 8
-        else:
-            return int(self.dtype[1:]) // 8
+        return int(self.dtype[1:]) // 8
 
 
 Registers = DotDict({
@@ -156,8 +156,6 @@ Registers = DotDict({
 })
 
 
-# pylama:ignore=E221
-
 class TraceMode(IntEnum):
     Analog         = 0
     Mixed          = 1
@@ -254,12 +252,12 @@ class VirtualMachine:
     class Transaction:
         def __init__(self, vm):
             self._vm = vm
+            self._data = b''
 
         def append(self, cmd):
             self._data += cmd
 
         async def __aenter__(self):
-            self._data = b''
             self._vm._transactions.append(self)
             return self
 
@@ -302,12 +300,12 @@ class VirtualMachine:
         else:
             self._transactions[-1].append(cmd)
 
-    async def read_replies(self, n):
+    async def read_replies(self, nreplies):
         if self._transactions:
             raise TypeError("Command transaction in progress")
         replies = []
         data, self._reply_buffer = self._reply_buffer, b''
-        while len(replies) < n:
+        while len(replies) < nreplies:
             index = data.find(b'\r')
             if index >= 0:
                 reply = data[:index]
@@ -333,25 +331,25 @@ class VirtualMachine:
 
     async def set_registers(self, **kwargs):
         cmd = ''
-        r0 = r1 = None
+        register0 = register1 = None
         for base, name in sorted((Registers[name].base, name) for name in kwargs):
             register = Registers[name]
-            bs = register.encode(kwargs[name])
-            Log.debug(f"{name} = 0x{''.join(f'{b:02x}' for b in reversed(bs))}")
-            for i, byte in enumerate(bs):
+            data = register.encode(kwargs[name])
+            Log.debug(f"{name} = 0x{''.join(f'{b:02x}' for b in reversed(data))}")
+            for i, byte in enumerate(data):
                 if cmd:
                     cmd += 'z'
-                    r1 += 1
+                    register1 += 1
                 address = base + i
-                if r1 is None or address > r1 + 3:
+                if register1 is None or address > register1 + 3:
                     cmd += f'{address:02x}@'
-                    r0 = r1 = address
+                    register0 = register1 = address
                 else:
-                    cmd += 'n' * (address - r1)
-                    r1 = address
-                if byte != r0:
+                    cmd += 'n' * (address - register1)
+                    register1 = address
+                if byte != register0:
                     cmd += '[' if byte == 0 else f'{byte:02x}'
-                    r0 = byte
+                    register0 = byte
         if cmd:
             await self.issue(cmd + 's')
 
@@ -384,22 +382,21 @@ class VirtualMachine:
     async def issue_triggered_trace(self):
         await self.issue(b'D')
 
-    async def read_analog_samples(self, n, sample_width):
+    async def read_analog_samples(self, nsamples, sample_width):
         if self._transactions:
             raise TypeError("Command transaction in progress")
         if sample_width == 2:
-            data = await self._reader.readexactly(2*n)
+            data = await self._reader.readexactly(2 * nsamples)
             return array.array('f', ((value+32768)/65536 for (value,) in struct.iter_unpack('>h', data)))
-        elif sample_width == 1:
-            data = await self._reader.readexactly(n)
+        if sample_width == 1:
+            data = await self._reader.readexactly(nsamples)
             return array.array('f', (value/256 for value in data))
-        else:
-            raise ValueError(f"Bad sample width: {sample_width}")
+        raise ValueError(f"Bad sample width: {sample_width}")
 
-    async def read_logic_samples(self, n):
+    async def read_logic_samples(self, nsamples):
         if self._transactions:
             raise TypeError("Command transaction in progress")
-        return await self._reader.readexactly(n)
+        return await self._reader.readexactly(nsamples)
 
     async def issue_cancel_trace(self):
         await self.issue(b'K')
@@ -413,15 +410,15 @@ class VirtualMachine:
     async def issue_wavetable_read(self):
         await self.issue(b'R')
 
-    async def wavetable_read_bytes(self, n):
+    async def wavetable_read_bytes(self, nbytes):
         if self._transactions:
             raise TypeError("Command transaction in progress")
-        return await self._reader.readexactly(n)
+        return await self._reader.readexactly(nbytes)
 
-    async def wavetable_write_bytes(self, bs):
+    async def wavetable_write_bytes(self, data):
         cmd = ''
         last_byte = None
-        for byte in bs:
+        for byte in data:
             if byte != last_byte:
                 cmd += f'{byte:02x}'
             cmd += 'W'