For working with Excel documents using Python, the `openpyxl` library is a popular choice. It allows you to read and write Excel 2010 xlsx/xlsm/xltx/xltm files, providing capabilities to create new worksheets, change cell values, apply styles, and much more. Below is a concise reference guide for common use cases with `openpyxl`, formatted in Markdown syntax:

# `openpyxl` Reference Guide

## Installation
```
pip install openpyxl
```

## Creating and Saving Workbooks
```python
from openpyxl import Workbook

# Create a new workbook
wb = Workbook()

# Save the workbook
wb.save('path_to_file.xlsx')
```

## Opening Existing Workbooks
```python
from openpyxl import load_workbook

# Load an existing workbook
wb = load_workbook('path_to_existing_file.xlsx')
```

## Working with Sheets
```python
# Create a new sheet
ws1 = wb.create_sheet(title="Sheet1")

# Select a sheet
ws2 = wb["Sheet1"]

# List all sheet names
sheets = wb.sheetnames

# Remove a sheet
del wb["Sheet1"]
```

## Writing to Cells
```python
# Select a cell
cell = ws1['A1']

# Assign a value to the cell
ws1['A1'] = 'Hello'
ws1.cell(row=2, column=2, value="World")

# Iterate over rows and columns
for row in range(1, 5):
    for col in range(1, 3):
        ws1.cell(row=row, column=col, value=f'Row {row}, Col {col}')
```

## Reading from Cells
```python
# Read a cell's value
value = ws1['A1'].value

# Iterate over rows and columns
for row in ws1.iter_rows(min_row=1, max_col=2, max_row=2):
    for cell in row:
        print(cell.value)
```

## Applying Styles
```python
from openpyxl.styles import Font, Color, Alignment, Border, Side

# Create a font style
font = Font(name='Calibri', size=12, bold=True, italic=False, color="FF0000")

# Apply the font to a cell
ws1['A1'].font = font

# Create and apply border style
border = Border(left=Side(border_style="thin", color="000000"),
                right=Side(border_style="thin", color="000000"),
                top=Side(border_style="thin", color="000000"),
                bottom=Side(border_style="thin", color="000000"))
ws1['A1'].border = border

# Apply alignment
alignment = Alignment(horizontal="center", vertical="center")
ws1['A1'].alignment = alignment
```

## Formulas
```python
# Assign a formula to a cell
ws1['A3'] = '=SUM(A1:A2)'
```

## Adding Charts
```python
from openpyxl.chart import BarChart, Reference

# Create data for the chart
for i in range(10):
    ws1.append([i])

# Create a bar chart
chart = BarChart()
data = Reference(ws1, min_col=1, min_row=1, max_col=1, max_row=10)
chart.add_data(data, titles_from_data=True)

# Add the chart to the sheet
ws1.add_chart(chart, "E5")
```

## Working with Rows and Columns
```python
# Insert a row at the second position
ws1.insert_rows(2)

# Delete the third row
ws1.delete_rows(3)

# Insert a column
ws1.insert_cols(2)

# Delete a column
ws1.delete_cols(3)

# Set row height
ws1.row_dimensions[1].height = 20

# Set column width
ws1.column_dimensions['A'].width = 30
```

## Save Changes
```python
wb.save('path_to_file.xlsx')
```

This guide covers the basics of creating and manipulating Excel files with `openpyxl`, including operations on workbooks and worksheets, cell manipulation, applying styles, and adding charts. These capabilities allow for robust Excel document generation and editing directly from Python scripts.