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| 1 | { | ||
| 2 | "cells": [ | ||
| 3 | { | ||
| 4 | "cell_type": "markdown", | ||
| 5 | "id": "637cdd40-65ae-43e5-8add-d60b89a5846c", | ||
| 6 | "metadata": {}, | ||
| 7 | "source": [ | ||
| 8 | "# Introduction to Python\n", | ||
| 9 | "\n", | ||
| 10 | "\n", | ||
| 11 | "## Goals\n", | ||
| 12 | "\n", | ||
| 13 | "- Present the Python programming language in a different way than [https://docs.python.org](https://docs.python.org)\n", | ||
| 14 | "\n", | ||
| 15 | "- Avoid information overload\n", | ||
| 16 | "\n", | ||
| 17 | "- Use examples and interaction rather than documents and slides\n", | ||
| 18 | "\n", | ||
| 19 | "\n", | ||
| 20 | "## Preliminary plan\n", | ||
| 21 | "\n", | ||
| 22 | "- **Basics: About the language, the Python eco-system, types, modules, functions, scopes, decorators, string formatting**\n", | ||
| 23 | "\n", | ||
| 24 | "- Object-oriented programming in Python: How Python \"really works\"\n", | ||
| 25 | "\n", | ||
| 26 | "- Control flow: if / for / while / try, iterators, \"tactical programming\" tips\n", | ||
| 27 | "\n", | ||
| 28 | "- A brief tour through Python's standard library\n", | ||
| 29 | "\n", | ||
| 30 | "- Code design and best practices: How to design your code" | ||
| 31 | ] | ||
| 32 | }, | ||
| 33 | { | ||
| 34 | "cell_type": "markdown", | ||
| 35 | "id": "5a72ab1d-f313-4f5f-93c7-60c1e07f8c22", | ||
| 36 | "metadata": {}, | ||
| 37 | "source": [ | ||
| 38 | "## What is Python?\n", | ||
| 39 | "\n", | ||
| 40 | "- Python is an interpreted high-level general-purpose programming language - advanced through the Python Enhancement Proposal (PEP) process\n", | ||
| 41 | "\n", | ||
| 42 | "- CPython is the reference implementation of Python, written in C (alternatives: pypy, jython)\n", | ||
| 43 | "\n", | ||
| 44 | "- python - interpreter and interpreter shell (alternatives: ipython, bpython)\n", | ||
| 45 | "\n", | ||
| 46 | "- libpython\n", | ||
| 47 | "\n", | ||
| 48 | "- Calling C from Python: Cython, CFFI, ctypes" | ||
| 49 | ] | ||
| 50 | }, | ||
| 51 | { | ||
| 52 | "cell_type": "markdown", | ||
| 53 | "id": "6d1edcfc-b001-4393-9c24-72adc9b5fccf", | ||
| 54 | "metadata": {}, | ||
| 55 | "source": [ | ||
| 56 | "## Philosophy\n", | ||
| 57 | "\n", | ||
| 58 | "```python\n", | ||
| 59 | "import this\n", | ||
| 60 | "```" | ||
| 61 | ] | ||
| 62 | }, | ||
| 63 | { | ||
| 64 | "cell_type": "code", | ||
| 65 | "execution_count": 96, | ||
| 66 | "id": "54c9e132-30b0-41bf-97e9-0e8b94f3d202", | ||
| 67 | "metadata": {}, | ||
| 68 | "outputs": [], | ||
| 69 | "source": [ | ||
| 70 | "import this" | ||
| 71 | ] | ||
| 72 | }, | ||
| 73 | { | ||
| 74 | "cell_type": "markdown", | ||
| 75 | "id": "4f144f73-51c1-419d-b71e-ee513f68f41c", | ||
| 76 | "metadata": {}, | ||
| 77 | "source": [ | ||
| 78 | "## Built-in functions\n", | ||
| 79 | "\n", | ||
| 80 | "Few built-in functions.\n", | ||
| 81 | "\n", | ||
| 82 | "[https://docs.python.org/3/library/functions.html](https://docs.python.org/3/library/functions.html)\n", | ||
| 83 | "\n", | ||
| 84 | "- `dir([obj])` - returns a list of valid attributes for that object\n", | ||
| 85 | "\n", | ||
| 86 | "- `id(obj)` - returns the \"identity\" of an object - an integer which is guaranteed to be unique\n", | ||
| 87 | "\n", | ||
| 88 | "- `print(...)` - prints objects to a text stream\n", | ||
| 89 | "\n", | ||
| 90 | "- `str(...)` - returns a string version of object\n", | ||
| 91 | "\n", | ||
| 92 | "- `type(obj)` - returns the type of an object" | ||
| 93 | ] | ||
| 94 | }, | ||
| 95 | { | ||
| 96 | "cell_type": "markdown", | ||
| 97 | "id": "a0c57535-e285-47af-80f9-1d4a16de5f25", | ||
| 98 | "metadata": {}, | ||
| 99 | "source": [ | ||
| 100 | "## Common built-in types\n", | ||
| 101 | "\n", | ||
| 102 | "Python uses duck typing and has typed objects but untyped variable names.\n", | ||
| 103 | "\n", | ||
| 104 | "Type constraints are not checked at compile time; rather, operations on an object may fail, signifying that the given object is not of a suitable type.\n", | ||
| 105 | "Despite being dynamically-typed, Python is strongly-typed, forbidding operations that are not well-defined (for example, adding a number to a string) rather than silently attempting to make sense of them.\n", | ||
| 106 | "\n", | ||
| 107 | "Variables / values must be of a certain type (class)." | ||
| 108 | ] | ||
| 109 | }, | ||
| 110 | { | ||
| 111 | "cell_type": "code", | ||
| 112 | "execution_count": 97, | ||
| 113 | "id": "bd6134d9-cc0e-4b45-b6b3-50210f6395e2", | ||
| 114 | "metadata": {}, | ||
| 115 | "outputs": [], | ||
| 116 | "source": [ | ||
| 117 | "# Common built-in types:\n", | ||
| 118 | "\n", | ||
| 119 | "s = 'foo' # this is a string / str, same as str('foo'), may be encoded, immutable (s[0] = 'r' is NOT possible)\n", | ||
| 120 | "\n", | ||
| 121 | "b = b'foo' # bytes, same as bytes('foo', 'utf-8'), may be decoded, immutable\n", | ||
| 122 | "\n", | ||
| 123 | "i = 6 # int, same as int('6'), immutable\n", | ||
| 124 | "\n", | ||
| 125 | "f = 0.1 # float, same as float('0.1'), immutable\n", | ||
| 126 | "\n", | ||
| 127 | "b = False # bool, same as bool(0), bool(''), bool(None)... immutable / constant\n", | ||
| 128 | "\n", | ||
| 129 | "n = None # NoneType, similar to 'null' in other languages, immutable / constant\n", | ||
| 130 | "\n", | ||
| 131 | "l = [1, False, 'foo'] # list, same as list((1, False, 'foo'))\n", | ||
| 132 | "\n", | ||
| 133 | "t = (1, False, 'foo') # tuple, same as tuple([1, False, 'foo']), immutable\n", | ||
| 134 | "\n", | ||
| 135 | "d = {'foo': 1, 'bar': 8} # dict, same as dict(foo=1, bar=8), similar to hash in other languages\n", | ||
| 136 | "\n", | ||
| 137 | "s = {'foo', 'bar', 1, 1, 4} # set, same as set(['foo', 'bar', 1, 1, 4]), removes duplicates" | ||
| 138 | ] | ||
| 139 | }, | ||
| 140 | { | ||
| 141 | "cell_type": "markdown", | ||
| 142 | "id": "6b2bc8fa-a5dc-4a58-92b2-abfb19bfe2ed", | ||
| 143 | "metadata": {}, | ||
| 144 | "source": [ | ||
| 145 | "## Modules\n", | ||
| 146 | "\n", | ||
| 147 | "A module is a file containing Python definitions and statements. The file name is the module name with the suffix *.py* appended. Within a module, the module's name (as a string) is available as the value of the global variable `__name__`\n", | ||
| 148 | "\n", | ||
| 149 | "When a module named *\"foo\"* is imported, the interpreter first searches for a built-in module with that name (`sys.builtin_module_names`). If not found, it then searches for a file named *foo.py* in a list of directories given by the variable `sys.path`. `sys.path` is initialized from these locations:\n", | ||
| 150 | "\n", | ||
| 151 | "- the directory containing the input script (or the current directory when no file is specified)\n", | ||
| 152 | "\n", | ||
| 153 | "- *PYTHONPATH* - env. variable - a list of directory names\n", | ||
| 154 | "\n", | ||
| 155 | "- the installation-dependent default locations\n", | ||
| 156 | "\n", | ||
| 157 | "The module is then imported only once and \"cached\" in `sys.modules`\n" | ||
| 158 | ] | ||
| 159 | }, | ||
| 160 | { | ||
| 161 | "cell_type": "markdown", | ||
| 162 | "id": "6c55e90b-9385-4ebd-90e9-e29654096287", | ||
| 163 | "metadata": {}, | ||
| 164 | "source": [ | ||
| 165 | "## Packages\n", | ||
| 166 | "\n", | ||
| 167 | "Packages are a way of structuring Python's module namespace by using \"dotted module names\"\n", | ||
| 168 | "\n", | ||
| 169 | "The import statement combines two operations:\n", | ||
| 170 | "\n", | ||
| 171 | "- it searches for the named module\n", | ||
| 172 | "\n", | ||
| 173 | "- it binds the results of that search to a name in the *local scope*\n", | ||
| 174 | "\n", | ||
| 175 | "\n", | ||
| 176 | "```python\n", | ||
| 177 | "# bar/__init__.py then bar.py will be considered, the first match executed and bound to 'bar'\n", | ||
| 178 | "import bar\n", | ||
| 179 | "\n", | ||
| 180 | "import mymodule.foo # implicitly executes mymodule/__init__.py (or mymodule.py) and mymodule/foo/__init__.py\n", | ||
| 181 | "\n", | ||
| 182 | "import numpy as np # will be bound as 'np' instead of 'numpy'. N.B. __name__ is still 'numpy'\n", | ||
| 183 | "\n", | ||
| 184 | "import some.extremely.deep.path.Animal as Animal # \"sacrifice\" the namespace in the name of convinience\n", | ||
| 185 | "\n", | ||
| 186 | "from sys import path # execute sys and only import the 'path' attribute into local scope as 'path'\n", | ||
| 187 | "\n", | ||
| 188 | "# relative imports must be explicit in Python 3\n", | ||
| 189 | "from .othermodule import something # expects that current module and 'othermodule' are in the same\n", | ||
| 190 | " # package (containing __init__.py)\n", | ||
| 191 | "\n", | ||
| 192 | "from sys import * # NO! Bad programming practice since 1879\n", | ||
| 193 | "```" | ||
| 194 | ] | ||
| 195 | }, | ||
| 196 | { | ||
| 197 | "cell_type": "markdown", | ||
| 198 | "id": "b26c4bd1-58ea-44bc-aedd-e6b6405da015", | ||
| 199 | "metadata": {}, | ||
| 200 | "source": [ | ||
| 201 | "## Creating and maintaining a Python environment\n", | ||
| 202 | "\n", | ||
| 203 | "Python's official package repository is PyPi [https://pypi.org](https://pypi.org), while Python's official package installer is *pip* [https://pypi.org/project/pip/](https://pypi.org/project/pip/)\n", | ||
| 204 | "\n", | ||
| 205 | "A Python environment is the physical and logical arrangement of Python modules and packages. Several options exist:\n", | ||
| 206 | "\n", | ||
| 207 | "- using a proper operating system :) (symlinks, real commercial support etc.)\n", | ||
| 208 | "\n", | ||
| 209 | "- using venv\n", | ||
| 210 | "\n", | ||
| 211 | "- using higher level tools like *poetry*\n", | ||
| 212 | "\n", | ||
| 213 | "- using a mixture / cocktail of all of the above :)" | ||
| 214 | ] | ||
| 215 | }, | ||
| 216 | { | ||
| 217 | "cell_type": "markdown", | ||
| 218 | "id": "40db50e4-fb7a-4a77-a074-bc4413f27212", | ||
| 219 | "metadata": {}, | ||
| 220 | "source": [ | ||
| 221 | "## Creating and maintaining a Python environment (cont...)\n", | ||
| 222 | "\n", | ||
| 223 | "Desired qualities for a flexible Python environment:\n", | ||
| 224 | "\n", | ||
| 225 | "- easy to create and (un)load\n", | ||
| 226 | "\n", | ||
| 227 | "- do not require extra privileges\n", | ||
| 228 | "\n", | ||
| 229 | "- don't repeat yourself (DRY)\n", | ||
| 230 | "\n", | ||
| 231 | "- easy to update without breaking the API\n", | ||
| 232 | "\n", | ||
| 233 | "- easy to debug\n", | ||
| 234 | "\n", | ||
| 235 | "- play nicely with the VCS (git)" | ||
| 236 | ] | ||
| 237 | }, | ||
| 238 | { | ||
| 239 | "cell_type": "markdown", | ||
| 240 | "id": "c661bf56-add0-402c-a629-a857f81d0758", | ||
| 241 | "metadata": {}, | ||
| 242 | "source": [ | ||
| 243 | "## Creating and maintaining a Python environment (cont...)\n", | ||
| 244 | "\n", | ||
| 245 | "Exploting the operating system can be done by:\n", | ||
| 246 | "\n", | ||
| 247 | "- (re)defining `PYTHONPATH`\n", | ||
| 248 | "- using symlinks to point at packages placed at different locations" | ||
| 249 | ] | ||
| 250 | }, | ||
| 251 | { | ||
| 252 | "cell_type": "markdown", | ||
| 253 | "id": "db8952aa-0944-4644-9626-7460786fd72a", | ||
| 254 | "metadata": {}, | ||
| 255 | "source": [ | ||
| 256 | "## Creating and maintaining a Python environment (cont...)\n", | ||
| 257 | "\n", | ||
| 258 | "Using venv can be done by directly invoking python:\n", | ||
| 259 | "\n", | ||
| 260 | "```bash\n", | ||
| 261 | "# create a virtual environment\n", | ||
| 262 | "python -m venv my_virtual_env\n", | ||
| 263 | "python -m venv --system-site-packages my_virtual_env\n", | ||
| 264 | "\n", | ||
| 265 | "# load, use and unload the virtual environment\n", | ||
| 266 | "source my_virtual_env/bin/activate\n", | ||
| 267 | "pip install sqlalchemy\n", | ||
| 268 | "# install package from a custom repository (https://artifactory.fifty.eu)\n", | ||
| 269 | "pip install --index-url=https://artifactory.fifty.eu/artifactory/api/pypi/pypi/simple/ odin-data-access\n", | ||
| 270 | "deactivate\n", | ||
| 271 | "\n", | ||
| 272 | "# one can alternatively use the python \"wrapper\" of the virtual env\n", | ||
| 273 | "my_virtual_env/bin/python -m pip install sqlalchemy\n", | ||
| 274 | "```\n", | ||
| 275 | "\n", | ||
| 276 | "*--system-site-packages* will keep the original *site-packages* folders at the end of `sys.path`" | ||
| 277 | ] | ||
| 278 | }, | ||
| 279 | { | ||
| 280 | "cell_type": "markdown", | ||
| 281 | "id": "299641e6-3d87-4a86-a124-eb49edb75b4b", | ||
| 282 | "metadata": {}, | ||
| 283 | "source": [ | ||
| 284 | "## Creating and maintaining a Python environment (cont...)\n", | ||
| 285 | "\n", | ||
| 286 | "Poetry [https://python-poetry.org](https://python-poetry.org) is the prefered environment and dependency management tool at Statnett.\n", | ||
| 287 | "\n", | ||
| 288 | "```bash\n", | ||
| 289 | "# create project and a virtual environment from scratch\n", | ||
| 290 | "poetry new my-project\n", | ||
| 291 | "\n", | ||
| 292 | "# ... or use Poetry with an existing one\n", | ||
| 293 | "cd my-project\n", | ||
| 294 | "poetry init\n", | ||
| 295 | "\n", | ||
| 296 | "# edit pyproject.toml for your needs (f.i. add dependencies, metadata ... etc),\n", | ||
| 297 | "# create virtual environment and install dependencies\n", | ||
| 298 | "poetry install\n", | ||
| 299 | "# it will create the file poetry.lock\n", | ||
| 300 | "# finally commit your poetry.lock file to version control\n", | ||
| 301 | "\n", | ||
| 302 | "# update all dependencies and poetry.lock\n", | ||
| 303 | "poetry update\n", | ||
| 304 | "```\n", | ||
| 305 | "\n", | ||
| 306 | "For more info: [https://python-poetry.org/docs/basic-usage/](https://python-poetry.org/docs/basic-usage/)" | ||
| 307 | ] | ||
| 308 | }, | ||
| 309 | { | ||
| 310 | "cell_type": "markdown", | ||
| 311 | "id": "a60540b1-ad17-4c40-88e1-e6d6af1ab219", | ||
| 312 | "metadata": {}, | ||
| 313 | "source": [ | ||
| 314 | "## Mutables vs. immutables\n", | ||
| 315 | "\n", | ||
| 316 | "Immutable object is an object with a fixed value. Immutable objects include `bool`, `int`, `float`, `str`, `bytes` and `tuple`. Such an object cannot be altered. A new object has to be created if a different value has to be stored. They play an important role in places where a constant hash value is needed, for example as a key in a dictionary.\n", | ||
| 317 | "\n", | ||
| 318 | "All objects that are not immutable are... mutable. All *hashable objects* **should** be immutable or use `id()`." | ||
| 319 | ] | ||
| 320 | }, | ||
| 321 | { | ||
| 322 | "cell_type": "code", | ||
| 323 | "execution_count": 98, | ||
| 324 | "id": "f4a4ea99-4038-4b61-9b8d-9ce623e6a663", | ||
| 325 | "metadata": {}, | ||
| 326 | "outputs": [ | ||
| 327 | { | ||
| 328 | "data": { | ||
| 329 | "text/plain": [ | ||
| 330 | "35041378544" | ||
| 331 | ] | ||
| 332 | }, | ||
| 333 | "execution_count": 98, | ||
| 334 | "metadata": {}, | ||
| 335 | "output_type": "execute_result" | ||
| 336 | }, | ||
| 337 | { | ||
| 338 | "data": { | ||
| 339 | "text/plain": [ | ||
| 340 | "35041378576" | ||
| 341 | ] | ||
| 342 | }, | ||
| 343 | "execution_count": 98, | ||
| 344 | "metadata": {}, | ||
| 345 | "output_type": "execute_result" | ||
| 346 | }, | ||
| 347 | { | ||
| 348 | "data": { | ||
| 349 | "text/plain": [ | ||
| 350 | "'H'" | ||
| 351 | ] | ||
| 352 | }, | ||
| 353 | "execution_count": 98, | ||
| 354 | "metadata": {}, | ||
| 355 | "output_type": "execute_result" | ||
| 356 | }, | ||
| 357 | { | ||
| 358 | "data": { | ||
| 359 | "text/plain": [ | ||
| 360 | "-6333845781340707986" | ||
| 361 | ] | ||
| 362 | }, | ||
| 363 | "execution_count": 98, | ||
| 364 | "metadata": {}, | ||
| 365 | "output_type": "execute_result" | ||
| 366 | }, | ||
| 367 | { | ||
| 368 | "data": { | ||
| 369 | "text/plain": [ | ||
| 370 | "36321214208" | ||
| 371 | ] | ||
| 372 | }, | ||
| 373 | "execution_count": 98, | ||
| 374 | "metadata": {}, | ||
| 375 | "output_type": "execute_result" | ||
| 376 | }, | ||
| 377 | { | ||
| 378 | "data": { | ||
| 379 | "text/plain": [ | ||
| 380 | "36321613808" | ||
| 381 | ] | ||
| 382 | }, | ||
| 383 | "execution_count": 98, | ||
| 384 | "metadata": {}, | ||
| 385 | "output_type": "execute_result" | ||
| 386 | }, | ||
| 387 | { | ||
| 388 | "data": { | ||
| 389 | "text/plain": [ | ||
| 390 | "27542959409390741" | ||
| 391 | ] | ||
| 392 | }, | ||
| 393 | "execution_count": 98, | ||
| 394 | "metadata": {}, | ||
| 395 | "output_type": "execute_result" | ||
| 396 | }, | ||
| 397 | { | ||
| 398 | "data": { | ||
| 399 | "text/plain": [ | ||
| 400 | "27542959409390741" | ||
| 401 | ] | ||
| 402 | }, | ||
| 403 | "execution_count": 98, | ||
| 404 | "metadata": {}, | ||
| 405 | "output_type": "execute_result" | ||
| 406 | } | ||
| 407 | ], | ||
| 408 | "source": [ | ||
| 409 | "i = 1\n", | ||
| 410 | "id(i) # returns f.i. 9788992\n", | ||
| 411 | "i += 1 # same as i = i + 1\n", | ||
| 412 | "id(i) # returns a different value, hence - a brand new object\n", | ||
| 413 | "\n", | ||
| 414 | "s = 'Hello'\n", | ||
| 415 | "s += ' World' # s is now a different object\n", | ||
| 416 | "s[0] # 'H'\n", | ||
| 417 | "# s[0] = 'h' # TypeError: 'str' object does not support item assignment\n", | ||
| 418 | "\n", | ||
| 419 | "t = (1, 4) # tuple\n", | ||
| 420 | "l = [1, 4] # list\n", | ||
| 421 | "hash(t) # returns f.i. -6333845781340707986\n", | ||
| 422 | "# hash(l) # TypeError: unhashable type: 'list'\n", | ||
| 423 | "\n", | ||
| 424 | "s = 'the long and winding road'\n", | ||
| 425 | "s2 = 'the long and winding road'\n", | ||
| 426 | "\n", | ||
| 427 | "# check if s and s2 are the same object:\n", | ||
| 428 | "id(s) # Out: 139858905258704\n", | ||
| 429 | "id(s2) # Out: 139858926037472\n", | ||
| 430 | "\n", | ||
| 431 | "# the hash should be the same\n", | ||
| 432 | "hash(s) # Out: 7030216208569256362\n", | ||
| 433 | "hash(s2) # Out: 7030216208569256362" | ||
| 434 | ] | ||
| 435 | }, | ||
| 436 | { | ||
| 437 | "cell_type": "markdown", | ||
| 438 | "id": "ba19a7d1-866c-40dc-ba9e-a04c8af5f1ba", | ||
| 439 | "metadata": {}, | ||
| 440 | "source": [ | ||
| 441 | "## Functions\n", | ||
| 442 | "\n", | ||
| 443 | "A function is a sequence of program instructions that performs a specific task, packaged as a unit.\n", | ||
| 444 | "\n", | ||
| 445 | "Functions let you:\n", | ||
| 446 | "\n", | ||
| 447 | "- reuse code across several programs / projects\n", | ||
| 448 | "\n", | ||
| 449 | "- minimize code duplication\n", | ||
| 450 | "\n", | ||
| 451 | "- devide larger programming tasks\n", | ||
| 452 | "\n", | ||
| 453 | "- hide implementation details\n", | ||
| 454 | "\n", | ||
| 455 | "- improve readability\n", | ||
| 456 | "\n", | ||
| 457 | "- improve traceability\n", | ||
| 458 | "\n", | ||
| 459 | "Function calls bring some overhead pushing / popping function-data into / from stack.\n", | ||
| 460 | "\n", | ||
| 461 | "Important definitions (may have different meanings in different programming languages):\n", | ||
| 462 | "\n", | ||
| 463 | "- *parameter / formal parameter* - variable / data provided as input to the function\n", | ||
| 464 | "\n", | ||
| 465 | "- *argument / actual parameter* - local variable / data to the given function\n", | ||
| 466 | "\n", | ||
| 467 | "The keyword `def` introduces a function definition." | ||
| 468 | ] | ||
| 469 | }, | ||
| 470 | { | ||
| 471 | "cell_type": "code", | ||
| 472 | "execution_count": 99, | ||
| 473 | "id": "bf95f44a-1257-440f-b35f-a8536c8c4363", | ||
| 474 | "metadata": {}, | ||
| 475 | "outputs": [ | ||
| 476 | { | ||
| 477 | "data": { | ||
| 478 | "text/plain": [ | ||
| 479 | "7" | ||
| 480 | ] | ||
| 481 | }, | ||
| 482 | "execution_count": 99, | ||
| 483 | "metadata": {}, | ||
| 484 | "output_type": "execute_result" | ||
| 485 | }, | ||
| 486 | { | ||
| 487 | "name": "stdout", | ||
| 488 | "output_type": "stream", | ||
| 489 | "text": [ | ||
| 490 | "9\n" | ||
| 491 | ] | ||
| 492 | }, | ||
| 493 | { | ||
| 494 | "data": { | ||
| 495 | "text/plain": [ | ||
| 496 | "[9, -2]" | ||
| 497 | ] | ||
| 498 | }, | ||
| 499 | "execution_count": 99, | ||
| 500 | "metadata": {}, | ||
| 501 | "output_type": "execute_result" | ||
| 502 | }, | ||
| 503 | { | ||
| 504 | "name": "stdout", | ||
| 505 | "output_type": "stream", | ||
| 506 | "text": [ | ||
| 507 | "[9, 5]\n" | ||
| 508 | ] | ||
| 509 | } | ||
| 510 | ], | ||
| 511 | "source": [ | ||
| 512 | "# Functions (example1)\n", | ||
| 513 | "\n", | ||
| 514 | "def add(a, b): # - function definition / header\n", | ||
| 515 | " \"\"\"Function for adding integers\"\"\" # - docstring\n", | ||
| 516 | " result = a + b\n", | ||
| 517 | " a = 5 # will not change the corresponding parameter since it is immutable\n", | ||
| 518 | " return result # - function that does not contain return, implicitly returns None\n", | ||
| 519 | "\n", | ||
| 520 | "a_param = 9\n", | ||
| 521 | "b_param = -2\n", | ||
| 522 | "add(a_param, b_param) # Out: 7\n", | ||
| 523 | "\n", | ||
| 524 | "# integers are immutable and a_param will remain unchanged\n", | ||
| 525 | "print(a_param) # Out: 9\n", | ||
| 526 | "\n", | ||
| 527 | "\n", | ||
| 528 | "def addl(a, b):\n", | ||
| 529 | " \"\"\"Function for adding two lists\"\"\"\n", | ||
| 530 | " result = a + b\n", | ||
| 531 | " a += [5] # in this case equal to: a.append(5)\n", | ||
| 532 | " return result\n", | ||
| 533 | "\n", | ||
| 534 | "a_param = [9]\n", | ||
| 535 | "b_param = [-2]\n", | ||
| 536 | "addl(a_param, b_param) # Out: [9, -2]\n", | ||
| 537 | "# lists are mutable and a_param will be changed\n", | ||
| 538 | "print(a_param) # Out: [9, 5]" | ||
| 539 | ] | ||
| 540 | }, | ||
| 541 | { | ||
| 542 | "cell_type": "code", | ||
| 543 | "execution_count": 100, | ||
| 544 | "id": "ecd03ee2-3523-40bd-afd1-4263a777bae0", | ||
| 545 | "metadata": {}, | ||
| 546 | "outputs": [], | ||
| 547 | "source": [ | ||
| 548 | "# Functions (example2) - parameters and arguments\n", | ||
| 549 | "\n", | ||
| 550 | "def add(a, b):\n", | ||
| 551 | " \"\"\"Function for adding integers\"\"\"\n", | ||
| 552 | " return a + b\n", | ||
| 553 | "\n", | ||
| 554 | "my_result = add(2, 5) # positional arguments (parameters)\n", | ||
| 555 | "my_result = add(b=5, a=2) # keyword arguments (parameters)\n", | ||
| 556 | "\n", | ||
| 557 | "my_tuple = (2, 5)\n", | ||
| 558 | "my_dict = {'b': 5, 'a': 2}\n", | ||
| 559 | "\n", | ||
| 560 | "my_result = add(*my_tuple) # unpacked and assigned to the positional arguments\n", | ||
| 561 | "my_result = add(**my_dict) # unpacked and assigned to the kw. arguments\n", | ||
| 562 | "\n", | ||
| 563 | "def add(a, b=5):\n", | ||
| 564 | " \"\"\"Function for adding integers\"\"\"\n", | ||
| 565 | " return a + b\n", | ||
| 566 | "my_result = add(2)\n", | ||
| 567 | "# ... and the rest of the examples above will work\n", | ||
| 568 | "\n", | ||
| 569 | "def add(a, *args, **kwargs):\n", | ||
| 570 | " \"\"\"Function for adding integers\"\"\"\n", | ||
| 571 | " if args:\n", | ||
| 572 | " b = args[0]\n", | ||
| 573 | " elif 'b' in kwargs:\n", | ||
| 574 | " b = kwargs['b']\n", | ||
| 575 | " return a + b\n", | ||
| 576 | "\n", | ||
| 577 | "my_result = add(2, 5, 9, 11) # 5 assigned to args[0]\n", | ||
| 578 | "my_result = add(2, b=5, c=9, d=11) # 5 assigned to kwargs['b']\n", | ||
| 579 | "\n", | ||
| 580 | "# my_result = add(2, b=5, 9, 11) # SyntaxError: positional argument follows keyword argument" | ||
| 581 | ] | ||
| 582 | }, | ||
| 583 | { | ||
| 584 | "cell_type": "markdown", | ||
| 585 | "id": "26a4f2fe-b79e-4e25-9107-230a53d11373", | ||
| 586 | "metadata": {}, | ||
| 587 | "source": [ | ||
| 588 | "## Functions (cont ...)\n", | ||
| 589 | "\n", | ||
| 590 | "Docstrings annotations and other hints\n", | ||
| 591 | "\n", | ||
| 592 | "```python\n", | ||
| 593 | "def decrypt(password: str, edata: str) -> str:\n", | ||
| 594 | " \"\"\"\n", | ||
| 595 | " Decrypts `edata` using `password`.\n", | ||
| 596 | "\n", | ||
| 597 | " `edata` is in the following format:\n", | ||
| 598 | " enc-val$`version-num`$`bas64-salt`$`base64-encrypted_data`\n", | ||
| 599 | "\n", | ||
| 600 | " :param password: The password to generate the key with\n", | ||
| 601 | " :type password: str\n", | ||
| 602 | "\n", | ||
| 603 | " :param edata: The data to be decrypted\n", | ||
| 604 | " :type edata: str\n", | ||
| 605 | "\n", | ||
| 606 | " :raises EtoolkitInstanceError: If the encryption format is unsupported\n", | ||
| 607 | "\n", | ||
| 608 | " :return: The output string / decrypted data\n", | ||
| 609 | " :rtype: str\n", | ||
| 610 | " \"\"\"\n", | ||
| 611 | " if not edata.startswith('enc-val$1$'):\n", | ||
| 612 | " raise EtoolkitInstanceError('Unsupported encryption format')\n", | ||
| 613 | " # some more code magic coming after....\n", | ||
| 614 | " # ...\n", | ||
| 615 | " # ..\n", | ||
| 616 | " return decrypted_str\n", | ||
| 617 | "```\n", | ||
| 618 | "\n", | ||
| 619 | "Using `typing` for more advanced / flexible hinting\n", | ||
| 620 | "\n", | ||
| 621 | "```python\n", | ||
| 622 | " \n", | ||
| 623 | "import typing\n", | ||
| 624 | "\n", | ||
| 625 | "Basestring = typing.Union[str, bytes]\n", | ||
| 626 | "\n", | ||
| 627 | "def decrypt(password: Basestring, edata: str) -> str:\n", | ||
| 628 | " pass\n", | ||
| 629 | "\n", | ||
| 630 | "\n", | ||
| 631 | "# or simply...\n", | ||
| 632 | "from typing import Union\n", | ||
| 633 | "\n", | ||
| 634 | "def decrypt(password: Union[str, bytes], edata: str) -> str:\n", | ||
| 635 | " \"\"\"Generic documentation. No need for pass\"\"\"\n", | ||
| 636 | "\n", | ||
| 637 | "# Python >= 3.10 only\n", | ||
| 638 | "def decrypt(password: str | bytes, edata: str) -> str:\n", | ||
| 639 | " \"\"\"Generic documentation. No need for pass\"\"\"\n", | ||
| 640 | "```" | ||
| 641 | ] | ||
| 642 | }, | ||
| 643 | { | ||
| 644 | "cell_type": "markdown", | ||
| 645 | "id": "40b749b3-5ec6-4c81-a9ee-3327433b4997", | ||
| 646 | "metadata": {}, | ||
| 647 | "source": [ | ||
| 648 | "## Functions (cont ...)\n", | ||
| 649 | "\n", | ||
| 650 | "Functions as parameters / arguments, lambdas and returning multiple values\n", | ||
| 651 | "\n", | ||
| 652 | "Functions in Python are callable objects. Callable objects can be created by defining the `__call__` method. More on that later in the course..." | ||
| 653 | ] | ||
| 654 | }, | ||
| 655 | { | ||
| 656 | "cell_type": "code", | ||
| 657 | "execution_count": 101, | ||
| 658 | "id": "edf9cfa7-d76c-428b-a39f-8c0697789031", | ||
| 659 | "metadata": {}, | ||
| 660 | "outputs": [], | ||
| 661 | "source": [ | ||
| 662 | "def fetch_the_first_letter(input_str: str) -> str:\n", | ||
| 663 | " \"\"\"Fetches the first letter of the string input_str or 'x'\"\"\"\n", | ||
| 664 | " try:\n", | ||
| 665 | " return input_str[0]\n", | ||
| 666 | " except Exception:\n", | ||
| 667 | " return 'x'\n", | ||
| 668 | "letter_list = list(map(fetch_the_first_letter, ['foo', 'bar', 'test'])) # Out: ['f', 'b', 't']\n", | ||
| 669 | "\n", | ||
| 670 | "\n", | ||
| 671 | "# Small anonymous functions can be created with the lambda keyword\n", | ||
| 672 | "letter_list = list(map(lambda x: x[0], ['foo', 'bar', 'test'])) # Out: ['f', 'b', 't']\n", | ||
| 673 | "\n", | ||
| 674 | "\n", | ||
| 675 | "# A function can return multiple values by implicitly returning a tuple:\n", | ||
| 676 | "\n", | ||
| 677 | "def square_cube(x):\n", | ||
| 678 | " \"\"\"returns x, x^2 and x^3\"\"\"\n", | ||
| 679 | " return x, x**2, x**3\n", | ||
| 680 | "\n", | ||
| 681 | "numbers = square_cube(5) # Out: (5, 25, 125)\n", | ||
| 682 | "num, sqnum, cbnum = square_cube(5) # unpacking the tuple" | ||
| 683 | ] | ||
| 684 | }, | ||
| 685 | { | ||
| 686 | "cell_type": "markdown", | ||
| 687 | "id": "d890df54-4097-43b5-a96d-1d9996e5626f", | ||
| 688 | "metadata": {}, | ||
| 689 | "source": [ | ||
| 690 | "## Functions (cont ...)\n", | ||
| 691 | "\n", | ||
| 692 | "Enclosing and nested functions\n", | ||
| 693 | "\n", | ||
| 694 | "Can be used as:\n", | ||
| 695 | "\n", | ||
| 696 | "- regular functions within functions\n", | ||
| 697 | "\n", | ||
| 698 | "- dynamic function factories" | ||
| 699 | ] | ||
| 700 | }, | ||
| 701 | { | ||
| 702 | "cell_type": "code", | ||
| 703 | "execution_count": 102, | ||
| 704 | "id": "ea583c17-c938-495a-9586-2027c66328a2", | ||
| 705 | "metadata": {}, | ||
| 706 | "outputs": [ | ||
| 707 | { | ||
| 708 | "name": "stdout", | ||
| 709 | "output_type": "stream", | ||
| 710 | "text": [ | ||
| 711 | "9\n", | ||
| 712 | "15\n" | ||
| 713 | ] | ||
| 714 | } | ||
| 715 | ], | ||
| 716 | "source": [ | ||
| 717 | "# enclosing functions\n", | ||
| 718 | "\n", | ||
| 719 | "def get_multiplier_of(base: int) -> str:\n", | ||
| 720 | " \"\"\"the function enclosing its nested functions\"\"\"\n", | ||
| 721 | "\n", | ||
| 722 | " def multiplier_function(x):\n", | ||
| 723 | " \"\"\"a nested function\"\"\"\n", | ||
| 724 | " return base * x\n", | ||
| 725 | "\n", | ||
| 726 | " return multiplier_function\n", | ||
| 727 | "\n", | ||
| 728 | "times3 = get_multiplier_of(3)\n", | ||
| 729 | "times5 = get_multiplier_of(5)\n", | ||
| 730 | "print(times3(3)) # Out: 9\n", | ||
| 731 | "print(times5(3)) # Out: 15" | ||
| 732 | ] | ||
| 733 | }, | ||
| 734 | { | ||
| 735 | "cell_type": "markdown", | ||
| 736 | "id": "cb5d1ad1-b702-41c3-92c4-93ed3df4e0c0", | ||
| 737 | "metadata": {}, | ||
| 738 | "source": [ | ||
| 739 | "## Scopes in Python\n", | ||
| 740 | "\n", | ||
| 741 | "- local - assigned names are local unless declared global\n", | ||
| 742 | "\n", | ||
| 743 | "- enclosed - the scope of the variable inside a function with a nested function\n", | ||
| 744 | "\n", | ||
| 745 | "- global - global for the current module\n", | ||
| 746 | "\n", | ||
| 747 | "- built-in\n", | ||
| 748 | "\n", | ||
| 749 | "`locals()` and `globals()` return dicts of symbols for their respective scopes" | ||
| 750 | ] | ||
| 751 | }, | ||
| 752 | { | ||
| 753 | "cell_type": "code", | ||
| 754 | "execution_count": 103, | ||
| 755 | "id": "49d7f6e1-1f54-4b96-8203-5eae95f47ebe", | ||
| 756 | "metadata": {}, | ||
| 757 | "outputs": [ | ||
| 758 | { | ||
| 759 | "name": "stdout", | ||
| 760 | "output_type": "stream", | ||
| 761 | "text": [ | ||
| 762 | "7 8\n", | ||
| 763 | "100\n", | ||
| 764 | "{'num3': 100, 'id': 200}\n", | ||
| 765 | "{}\n", | ||
| 766 | "{}\n", | ||
| 767 | "99\n" | ||
| 768 | ] | ||
| 769 | } | ||
| 770 | ], | ||
| 771 | "source": [ | ||
| 772 | "num1, num2 = 7, 8 # module globals\n", | ||
| 773 | "\n", | ||
| 774 | "def print_numbers():\n", | ||
| 775 | " print(num1, num2) # OK, these are module globals\n", | ||
| 776 | " num3 = 100\n", | ||
| 777 | " print(num3) # prints 100, num3 is in the function (local) scope\n", | ||
| 778 | " global num4 # assignes / references num4 to / in the global scope\n", | ||
| 779 | " num4 = 99\n", | ||
| 780 | " id = 200 # new symbol in local scope\n", | ||
| 781 | " # id(num4) # will not yield the expected result (raises TypeError)\n", | ||
| 782 | " print(locals())\n", | ||
| 783 | "\n", | ||
| 784 | " def print_numbers2():\n", | ||
| 785 | " print(locals())\n", | ||
| 786 | " # print(num3) # OK, enclosed scope\n", | ||
| 787 | " print(locals())\n", | ||
| 788 | "\n", | ||
| 789 | " print_numbers2() # prints 100\n", | ||
| 790 | "\n", | ||
| 791 | "print_numbers()\n", | ||
| 792 | "# print(num3) # Raises NameError - why?\n", | ||
| 793 | "print(num4) # Prints 99 - why?\n", | ||
| 794 | "# print_numbers2() # Raises NameError" | ||
| 795 | ] | ||
| 796 | }, | ||
| 797 | { | ||
| 798 | "cell_type": "markdown", | ||
| 799 | "id": "5c91e152-a658-4811-832f-90712d708f8d", | ||
| 800 | "metadata": {}, | ||
| 801 | "source": [ | ||
| 802 | "## Decorators\n", | ||
| 803 | "\n", | ||
| 804 | "Decorators can be used to modify the behavior of the objects they decorate. Decorators can be implemented either by using classes or by using nested functions.\n", | ||
| 805 | "\n", | ||
| 806 | "```python \n", | ||
| 807 | "def my_decorator(func):\n", | ||
| 808 | "\n", | ||
| 809 | " def decorated():\n", | ||
| 810 | " print('Doing something before the decorated function')\n", | ||
| 811 | " retval = func()\n", | ||
| 812 | " print('Doing something after the decorated function')\n", | ||
| 813 | " return retval\n", | ||
| 814 | " return decorated\n", | ||
| 815 | "\n", | ||
| 816 | "def my_function():\n", | ||
| 817 | " print('Alice')\n", | ||
| 818 | "\n", | ||
| 819 | "my_function = my_decorator(my_function)\n", | ||
| 820 | "my_function()\n", | ||
| 821 | "``` \n", | ||
| 822 | "\n", | ||
| 823 | "... may be dificult to read / understand, while:\n", | ||
| 824 | "\n", | ||
| 825 | "```python \n", | ||
| 826 | "@my_decorator\n", | ||
| 827 | "def my_function():\n", | ||
| 828 | " print('Alice')\n", | ||
| 829 | "\n", | ||
| 830 | "my_function()\n", | ||
| 831 | "``` \n", | ||
| 832 | "\n", | ||
| 833 | "... may be easier" | ||
| 834 | ] | ||
| 835 | }, | ||
| 836 | { | ||
| 837 | "cell_type": "code", | ||
| 838 | "execution_count": 104, | ||
| 839 | "id": "4346260d-76af-437e-9c10-1c1d0c478695", | ||
| 840 | "metadata": {}, | ||
| 841 | "outputs": [], | ||
| 842 | "source": [ | ||
| 843 | "# Decorators (cont ...) - a complete example\n", | ||
| 844 | "\n", | ||
| 845 | "import sys\n", | ||
| 846 | "from functools import wraps\n", | ||
| 847 | "\n", | ||
| 848 | "def requires_access(access_secret: str):\n", | ||
| 849 | "\n", | ||
| 850 | " def api_access_decorator(f):\n", | ||
| 851 | "\n", | ||
| 852 | " @wraps(f)\n", | ||
| 853 | " def decorated(*args, **kwargs):\n", | ||
| 854 | " if 'secret' not in kwargs:\n", | ||
| 855 | " sys.exit('No secret provided')\n", | ||
| 856 | " if not kwargs['secret'] or kwargs['secret'] != access_secret:\n", | ||
| 857 | " sys.exit(\"Secret doesn't match\")\n", | ||
| 858 | " # return f(args[0], **kwargs)\n", | ||
| 859 | " return f(*args, **kwargs)\n", | ||
| 860 | "\n", | ||
| 861 | " return decorated\n", | ||
| 862 | "\n", | ||
| 863 | " return api_access_decorator\n", | ||
| 864 | "\n", | ||
| 865 | "\n", | ||
| 866 | "@requires_access(access_secret='b28cfeaa65b73cf')\n", | ||
| 867 | "def sensitive_function(data, **kwargs):\n", | ||
| 868 | " \"\"\"very sensitive function\"\"\"\n", | ||
| 869 | " db.save(data)" | ||
| 870 | ] | ||
| 871 | }, | ||
| 872 | { | ||
| 873 | "cell_type": "markdown", | ||
| 874 | "id": "14ea817a-0748-4941-8899-0b9025f25a93", | ||
| 875 | "metadata": {}, | ||
| 876 | "source": [ | ||
| 877 | "## String formatting\n", | ||
| 878 | "\n", | ||
| 879 | "The old ways...\n", | ||
| 880 | "\n", | ||
| 881 | "```python \n", | ||
| 882 | "f = 6.57865\n", | ||
| 883 | "i = 27\n", | ||
| 884 | "s = 'another string'\n", | ||
| 885 | "\n", | ||
| 886 | "\n", | ||
| 887 | "'%s - %d - %5.2f' % (s, i, f) # Out: 'another string - 27 - 6.58'\n", | ||
| 888 | "\n", | ||
| 889 | "# still used in:\n", | ||
| 890 | "logger.debug(\"%d - %s\", event.id, message)\n", | ||
| 891 | "\n", | ||
| 892 | "# using the .format method\n", | ||
| 893 | "'{} - {} - {:5.2f}'.format(s, i, f) # implicit\n", | ||
| 894 | "'{0} - {1} - {2:5.2f}'.format(s, i, f) # explicit\n", | ||
| 895 | "'{my_str} - {i} - {fl:5.2f}'.format(my_str=s, fl=f, i=i) # keyword\n", | ||
| 896 | "# Out: 'another string - 27 - 6.58'\n", | ||
| 897 | "\n", | ||
| 898 | "\n", | ||
| 899 | "# modern Python >= 3.6 f-strings\n", | ||
| 900 | "f'{s} - {i} - {f:5.2f}' # Out: 'another string - 27 - 6.58'\n", | ||
| 901 | "``` \n", | ||
| 902 | "\n", | ||
| 903 | "See https://docs.python.org/3/library/string.html#formatspec for the complete format specification" | ||
| 904 | ] | ||
| 905 | } | ||
| 906 | ], | ||
| 907 | "metadata": { | ||
| 908 | "kernelspec": { | ||
| 909 | "display_name": "Python 3 (ipykernel)", | ||
| 910 | "language": "python", | ||
| 911 | "name": "python3" | ||
| 912 | }, | ||
| 913 | "language_info": { | ||
| 914 | "codemirror_mode": { | ||
| 915 | "name": "ipython", | ||
| 916 | "version": 3 | ||
| 917 | }, | ||
| 918 | "file_extension": ".py", | ||
| 919 | "mimetype": "text/x-python", | ||
| 920 | "name": "python", | ||
| 921 | "nbconvert_exporter": "python", | ||
| 922 | "pygments_lexer": "ipython3", | ||
| 923 | "version": "3.10.8" | ||
| 924 | } | ||
| 925 | }, | ||
| 926 | "nbformat": 4, | ||
| 927 | "nbformat_minor": 5 | ||
| 928 | } | ||