Python

pip

Update pip (ref):
[Mac] pip install -U pip
[Windows] python -m pip install -U pip

Update package: pip install [package_name] --upgrade

docstring

def complex(real=0.0, imag=0.0):
    """Form a complex number.

    Keyword arguments:
    real -- the real part (default 0.0)
    imag -- the imaginary part (default 0.0)
    """

Input

User input

input(prompt)

Files

Copy file: shutil.copy2(fullpath, fullpath_copy)

Delete file: os.remove(fullpath)

Read/write to files: docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files

with open('workfile') as f:
    for line in f:
        print(line, end='')

CSV files

csv

with open(filepath, newline='') as f:
    reader = csv.reader(f)
    for row in reader:
        # do something

List/dict/set comprehensions

list_comp = [expr for val in collection if condition]
dict_comp = {key-expr : value-expr for value in collection if condition}
set_comp = {expr for value in collection if condition}

Operating system interfaces

os

Walk through directory tree:

for root, dirs, files in os.walk(start_dir):
    # do something

Create directory if it doesn't exist (via SO):

os.makedirs("path/to/directory", exist_ok=True)

os.path

Base user directory: os.path.expanduser('~')

Datetime

string to datetime: datetime.strptime()

datetime to string: datetime.strftime()

openpyxl

Documentation

Load workbook: wb = load_workbook(filename=fullpath, read_only=True)

Loop over rows in worksheet:

for row in ws.rows:
    for col in row:
        v = row[col].value

Plotting

# Draw an ellipse using parametric equations
# Source: https://stackoverflow.com/a/48409811/752784
import numpy
from matplotlib import pyplot
from math import pi
x_0 = 1.0
y_0 = 0.5
a = 2.0    # semimajor axis
b = 1.5    # semiminor axis
t = numpy.linspace(0, 2 * pi, 100)
pyplot.plot(x_0 + a * numpy.cos(t), y_0 + b * numpy.sin(t))
pyplot.show()

# Draw a random path

import numpy
import matplotlib.pyplot as pyplot

# Add random number of points
import random
n = random.randint(5,10)
points = numpy.zeros((n,2))

for i in range(n):
    # Add random points
    a = random.randint(1,10)
    b = random.randint(1,10)
    points[i,:] = [a, b]

# Complete the loop: repeat first point as last point
# Appending to numpy arrays: https://stackoverflow.com/a/42545300/752784
points = numpy.append(points, [points[0,:]], axis=0)

pyplot.plot(points[:,0], points[:,1])
pyplot.show()

Pandas

From Chris Moffitt, Tips for Selecting Columns in a DataFrame, Practical Business Python, 2019-11-26:

df = pd.read_csv(
    'https://data.cityofnewyork.us/api/views/vfnx-vebw/rows.csv?accessType=DOWNLOAD&bom=true&format=true'
)
col_mapping_dict = {c[0]:c[1] for c in enumerate(df.columns)}
df.iloc[:, np.r_[0:3,15:19,24,25]]

Trees

treelib

tkinter

Dialogs

tkinter.simpledialog, tkinter.filedialog, tkinter.commondialog

Simple file selection (inspired by)

from tkinter import Tk
from tkinter.filedialog import askopenfilename
import os.path
import pandas as pd
def load_data_file():
        Tk().withdraw()
        data_filepath = askopenfilename()
        data_filename = os.path.split(data_filepath)[1]
        ext = os.path.splitext(data_filename)[1]
        
        if ext == '.xlsx' or ext == '.xls':
            df = pd.read_excel(data_filepath)
        elif ext == '.csv':
            df = pd.read_csv(data_filepath)
            
        return df

Miscellaneous

Pyperclip

pyperclip.copy('Hello, world!')

Kirk Kittell

Res ipsa loquitur. Let the good times roll.