Initial commit of PyCon 2018 talk slides and material.

.gitignore

@@ -0,0 +1,105 @@
+
+# Created by https://www.gitignore.io/api/python
+
+### Python ###
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.coverage.*
+.cache
+.pytest_cache/
+nosetests.xml
+coverage.xml
+*.cover
+.hypothesis/
+
+# Translations
+*.mo
+*.pot
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# pyenv
+.python-version
+
+# celery beat schedule file
+celerybeat-schedule.*
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+
+
+# End of https://www.gitignore.io/api/python

README.md

@@ -0,0 +1,6 @@
+# Python Performance Investigation by Example
+
+Slides [here](./presentation/Python Performance Investigation - PyCon 2018.pdf).
+
+Use `snakeviz slow_mode.cprof` to see the SnakeViz profile demo'd in the talk.
+(Requires Python 3.)

day13/input.txt

@@ -0,0 +1,43 @@
+0: 3
+1: 2
+2: 4
+4: 6
+6: 4
+8: 6
+10: 5
+12: 6
+14: 9
+16: 6
+18: 8
+20: 8
+22: 8
+24: 8
+26: 8
+28: 8
+30: 12
+32: 14
+34: 10
+36: 12
+38: 12
+40: 10
+42: 12
+44: 12
+46: 12
+48: 12
+50: 12
+52: 14
+54: 14
+56: 12
+62: 12
+64: 14
+66: 14
+68: 14
+70: 17
+72: 14
+74: 14
+76: 14
+82: 14
+86: 18
+88: 14
+96: 14
+98: 44

fast_mode.py

@@ -0,0 +1,46 @@
+import itertools
+
+
+def puzzle_input() -> dict:
+    with open('./day13/input.txt') as f:
+        return {
+            layer: range_
+            for layer, range_ in (
+                map(int, row.strip().split(': ')) for row in f)}
+
+
+def scanner_layer(scanner_height: int, time_step: int) -> int:
+    """
+    Calculates the position of a scanner within its range at a
+    given time step.
+
+    """
+    cycle_midpoint = scanner_height - 1
+    full_cycle = cycle_midpoint * 2
+    cycle_position = time_step % full_cycle
+    return (
+        cycle_position
+        if cycle_position <= cycle_midpoint
+        else full_cycle - cycle_position)
+
+
+def check_capture(firewall: dict, num_layers: int, t_start: int) -> bool:
+    """Returns True if the packet is caught while crossing, otherwise False."""
+    for pos in range(num_layers):
+        if pos in firewall:
+            scanner_height = firewall[pos]
+            scanner_pos = scanner_layer(scanner_height, t_start + pos)
+            if scanner_pos == 0:
+                return True
+    return False
+
+
+def find_start(firewall: dict) -> int:
+    num_layers = max(firewall.keys()) + 1
+    for t_start in itertools.count(0):
+        if not check_capture(firewall, num_layers, t_start):
+            break
+    return t_start
+
+
+print(find_start(puzzle_input()))

slow_mode.py

@@ -0,0 +1,94 @@
+import itertools
+from typing import Dict, Iterator
+
+
+class Scanner:
+    """Holds the state of a single scanner."""
+    def __init__(self, layer: int, range_: int):
+        self.layer = layer
+        self.range_ = range_
+        self.pos = 0
+        self.dir_ = 'down'
+
+    def advance(self):
+        """Advance this scanner one time step."""
+        if self.dir_ == 'down':
+            self.pos += 1
+            if self.pos == self.range_ - 1:
+                self.dir_ = 'up'
+        else:
+            self.pos -= 1
+            if self.pos == 0:
+                self.dir_ = 'down'
+
+    def copy(self):
+        """Make a copy of this scanner in the same state."""
+        inst = self.__class__(self.layer, self.range_)
+        inst.pos = self.pos
+        inst.dir_ = self.dir_
+        return inst
+
+
+def init_firewall(rows: Iterator[str]) -> Dict[int, Scanner]:
+    """Create a dictionary of scanners from the puzzle input."""
+    firewall = {}
+    for row in rows:
+        layer, range_ = (int(x) for x in row.split(': '))
+        firewall[layer] = Scanner(layer, range_)
+    return firewall
+
+
+def puzzle_input() -> Dict[int, Scanner]:
+    """Helper for loading puzzle input."""
+    with open('./day13/input.txt') as f:
+        return init_firewall(f)
+
+
+def check_capture(
+        firewall: Dict[int, Scanner], num_layers: int) -> bool:
+    """Returns True if the packet is caught while crossing, otherwise False."""
+    for packet_pos in range(num_layers):
+        # check if the scanner is captured in this position
+        if packet_pos in firewall and firewall[packet_pos].pos == 0:
+            return True
+
+        # advance scanners to their next positions
+        for scanner in firewall.values():
+            scanner.advance()
+
+    return False
+
+
+def copy_firewall(
+        firewall: Dict[int, Scanner]) -> Dict[int, Scanner]:
+    """Make a copy of a firewall dictionary"""
+    return {
+        layer: scanner.copy() for layer, scanner in firewall.items()
+    }
+
+
+def find_start(firewall: Dict[int, Scanner]) -> int:
+    """Attempt crossing until we make it uncaught."""
+    loop_firewall = copy_firewall(firewall)
+    num_layers = max(firewall.keys()) + 1
+
+    for t_start in itertools.count(0):
+        # save the state of the firewall before we start to cross
+        # so we can use it as the basis of a potential next attempt
+        pre_check_firewall = copy_firewall(loop_firewall)
+
+        # check if the packet is caught while attempting a crossing starting
+        # at this time step
+        if check_capture(loop_firewall, num_layers):
+            # reset to pre-check state and advance once
+            # so we can attempt a crossing at the next timestep
+            loop_firewall = copy_firewall(pre_check_firewall)
+            for scanner in loop_firewall.values():
+                scanner.advance()
+        else:
+            break
+
+    return t_start
+
+
+print(find_start(puzzle_input()))