Python Basic Memo

Official Documentation

• 3.9.2 Documentation
• The Python Tutorial — Python 3.9.4 documentation

General

• __import__('keyword').kwlist 予約語
• dir(__builtins__) Builtin関数

string

• Pythonの文字列フォーマット（formatメソッドの使い方） | ガンマソフト株式会社 まとまってる、ありがたし。

file

• os.path — Common pathname manipulations — Python 3.9.2 documentation
• os.path.join(path, *paths) pathをくっつける。
• os.path.basename(path) pathからファイル名だけとる。
• os.path.exists(path), os.path.isdir(path), os.path.isfile(path) 存在確認

• os — Miscellaneous operating system interfaces — Python 3.9.2 documentation
• os.environ['HOME'] 環境変数
• os.makedirs(name, mode=0o777, exist_ok=False)
  • Recursive directory creation function. Like mkdir(), but makes all intermediate-level directories needed to contain the leaf directory. 再帰的. mkdir -p
• os.walk(top) ディレクトリを捜査 => (dirpath, dirnames, filenames) dirnamesとfilenamesはlist。次の例が良い。
  • python - Do I understand os.walk right? - Stack Overflow

• 6. Modules — Python 3.9.2 documentation
  • sys.path => The module search path

• shutil — High-level file operations — Python 3.9.2 documentation
• shutil.copy(src, dst, *, follow_symlinks=True) コピー
• shutil.move(src, dst, copy_function=copy2)

• glob — Unix style pathname pattern expansion — Python 3.9.2 documentation

glob.glob('*.gif')
['1.gif', 'card.gif']

function

• 4. More Control Flow Tools — Python 3.9.2 documentation Keyword Arguments

Definition

def cheeseshop(kind, *arguments, **keywords):
    print("-- Do you have any", kind, "?")
    print("-- I'm sorry, we're all out of", kind)
    for arg in arguments:
        print(arg)
    print("-" * 40)
    for kw in keywords:
        print(kw, ":", keywords[kw])

Input

cheeseshop("Limburger", "It's very runny, sir.",
           "It's really very, VERY runny, sir.",
           shopkeeper="Michael Palin",
           client="John Cleese",
           sketch="Cheese Shop Sketch")

Output

-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
shopkeeper : Michael Palin
client : John Cleese
sketch : Cheese Shop Sketch

argparse

• argparse — Parser for command-line options, arguments and sub-commands — Python 3.9.2 documentation

datetime

• datetime — Basic date and time types — Python 3.9.2 documentation
• datetime — Basic date and time types — Python 3.9.2 documentation Format codes
• strftime(format) datetime => str. 諸説ある from, format
• strptime(date_string, format) str => datetime. 諸説ある parse, points
• timedeltaのsecondsとtotal_seconds()

datetime.timedelta(days=1).seconds # => 0
datetime.timedelta(days=1).total_seconds() # => 86400.0

json

• json — JSON encoder and decoder — Python 3.9.2 documentation
• dump()はファイルfpへ、dumps()はstrへ。
• load()はファイルfpから、loads()はstrから。sってstrのsだったのか。

re

• re — Regular expression operations — Python 3.9.2 documentation

requests

• Requests: HTTP for Humans™ — Requests 2.25.1 documentation
• Quickstart — Requests 2.25.1 documentation ここを読めばOK.

Psycopg – PostgreSQL database adapter

• Psycopg – PostgreSQL database adapter for Python — Psycopg 2.8.7.dev0 documentation
• Installation — Psycopg 2.8.7.dev0 documentation 基本的な使い方
• python - How do I get a list of column names from a psycopg2 cursor? - Stack Overflow 列名

colnames = [desc[0] for desc in curs.description]

logging

• Logging HOWTO — Python 3.9.2 documentation
  • 何もしていないとconsoleに。filenameを指定するとファイルに。

import logging
logging.warning('Watch out!')  # will print a message to the console
logging.info('I told you so')  # will not print anything

import logging
logging.basicConfig(filename='example.log', encoding='utf-8', level=logging.DEBUG)
logging.debug('This message should go to the log file')
logging.info('So should this')
logging.warning('And this, too')
logging.error('And non-ASCII stuff, too, like Øresund and Malmö')

• python - logger configuration to log to file and print to stdout - Stack Overflow
  • Consoleにもファイルにも出したい時。

import logging
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(levelname)s] %(message)s",
    handlers=[
        logging.FileHandler("debug.log"),
        logging.StreamHandler()
    ]
)

• Redirect stdout to a file in Python? - Stack Overflow 邪道

import sys
sys.stdout = open('file', 'w')
print('test')

Jupyter notebook

• %quickref
• Display all dataframe columns in a Jupyter Python Notebook - Stack Overflow
  • pandasのdataframeをfullでdisplay
• python - Pop-out / expand jupyter cell to new browser window - Stack Overflow
  • pandasのdataframeを別windowsで。

misc

• importlib — The implementation of import — Python 3.9.2 documentation
  • ファイル名でimportしたい。importlib.import_module なんか思てたんと違う。ちゃんと読もう。
• python - Lists in ConfigParser - Stack Overflow
  • configParserでlist。