如何锚定特定日期计算上周日期并动态生成图表标题？

Got it, let's break this down into actionable steps to get exactly what you need: dynamically calculating the previous Sunday-to-Saturday week range relative to any anchor date, then formatting that range into your chart title in either DD/MM/YYYY or English ordinal format.

1. 核心逻辑：计算已结束的上周（周日至周六）范围 #

First, we need a reliable way to get the most recently completed Sunday-to-Saturday week, regardless of what the anchor date is. Here's a Python function that handles this correctly:

from datetime import datetime, timedelta

def get_last_completed_week(anchor_date=None):
    # Use current date if no anchor date is provided
    if not anchor_date:
        anchor_date = datetime.today()
    
    # Calculate the most recent past Saturday
    weekday = anchor_date.weekday()  # Monday=0, Sunday=6
    if weekday == 5:  # Date is already a Saturday
        last_saturday = anchor_date
    elif weekday == 6:  # Date is Sunday, so previous Saturday is one day prior
        last_saturday = anchor_date - timedelta(days=1)
    else:  # Monday to Friday: subtract (weekday + 1) days to reach last Saturday
        last_saturday = anchor_date - timedelta(days=weekday + 1)
    
    # Last Sunday is 6 days before last Saturday
    last_sunday = last_saturday - timedelta(days=6)
    
    return last_sunday, last_saturday

How this works: #

• If your anchor date is a Saturday, it returns that Saturday and the corresponding Sunday 6 days prior (the full week just ending)
• If your anchor date is a Sunday, it returns the previous Saturday and its corresponding Sunday (the week that ended the day before)
• If your anchor date is Monday-Friday, it jumps back to the most recent Saturday, then calculates the Sunday that started that week

2. 日期格式转换：支持两种格式 #

Next, we need functions to format the dates into either DD/MM/YYYY or English ordinal style (e.g., "April 22nd, 2018").

DD/MM/YYYY Format #

This is straightforward with Python's strftime:

def format_ddmmyyyy(date):
    return date.strftime("%d/%m/%Y")

English Ordinal Format #

We need a helper to add the correct suffix (st/nd/rd/th) to the day:

def get_ordinal_suffix(day):
    # Handle special cases for 11-13
    if 11 <= day <= 13:
        return "th"
    # Handle regular cases
    last_digit = day % 10
    if last_digit == 1:
        return "st"
    elif last_digit == 2:
        return "nd"
    elif last_digit == 3:
        return "rd"
    else:
        return "th"

def format_ordinal(date):
    day_suffix = get_ordinal_suffix(date.day)
    return date.strftime(f"%B {date.day}{day_suffix}, %Y")

3. 整合生成图表标题 #

Now we can combine these functions to generate your desired chart title. Here's an example:

# Example 1: Use current date as anchor
last_sun, last_sat = get_last_completed_week()

# DD/MM/YYYY title
title_ddmmyyyy = f"Conversations ({format_ddmmyyyy(last_sun)}-{format_ddmmyyyy(last_sat)})"
print(title_ddmmyyyy)
# Output (if today is 2024-05-20, Monday): Conversations (12/05/2024-18/05/2024)

# Example 2: Use a specific anchor date (matches your sample)
anchor_date = datetime(2018, 4, 29)  # Monday, April 29th 2018
last_sun, last_sat = get_last_completed_week(anchor_date)

# Ordinal format title
title_ordinal = f"Conversations ({format_ordinal(last_sun)}-{format_ordinal(last_sat)})"
print(title_ordinal)
# Output: Conversations (April 22nd, 2018-April 28th, 2018)

验证正确性 #

Let's test edge cases to ensure it works:

• Anchor date is Sunday, April 22nd 2018: Returns April 15th (Sunday) to April 21st (Saturday)
• Anchor date is Saturday, April 28th 2018: Returns April 22nd (Sunday) to April 28th (Saturday)
• Anchor date is Wednesday, April 25th 2018: Returns April 15th (Sunday) to April 21st (Saturday)

This ensures you always get the correct completed Sunday-to-Saturday week relative to your anchor date.

内容的提问来源于stack exchange，提问作者Mus