日期格式转换报错：将%d/%m/%Y转为%-d-%b-%Y时触发ValueError

错误原因 #

问题出在%-d格式符上：它是POSIX系统（Linux/macOS）专属的语法，用于去除日期数字前的前导零（比如将05转为5），但Windows系统的strftime不支持该写法，因此触发ValueError: Invalid format string。

方案1：跨平台兼容写法 #

通过判断当前操作系统，匹配对应格式符：

from datetime import datetime
import sys
from tkinter import *
from tkcalendar import DateEntry

win = Tk()
win.geometry("750x250")
win.title("Example")

def convert():
    date1 = cal.get()
    datetimeobject = datetime.strptime(date1, '%d/%m/%Y')
    print(date1)
    # 根据系统选择对应格式符
    if sys.platform.startswith('win'):
        new_format = datetimeobject.strftime('%#d-%b-%Y')
    else:
        new_format = datetimeobject.strftime('%-d-%b-%Y')
    print(new_format)

cal = DateEntry(win, width=16, background="gray61", foreground="white", bd=2, date_pattern='dd/mm/y')
cal.pack(pady=20)

btn = Button(win, command=convert, text='PRESS')
btn.pack(pady=50)

win.mainloop()

方案2：字符串处理去除前导零（无需判断系统） #

先生成带前导零的格式字符串，再手动去除日期部分的前导零：

from datetime import datetime
from tkinter import *
from tkcalendar import DateEntry

win = Tk()
win.geometry("750x250")
win.title("Example")

def convert():
    date1 = cal.get()
    datetimeobject = datetime.strptime(date1, '%d/%m/%Y')
    print(date1)
    # 先生成带前导零的格式，拆分后处理日期部分
    temp_format = datetimeobject.strftime('%d-%b-%Y')
    day, rest = temp_format.split('-', 1)
    new_format = f"{int(day)}-{rest}"
    print(new_format)

cal = DateEntry(win, width=16, background="gray61", foreground="white", bd=2, date_pattern='dd/mm/y')
cal.pack(pady=20)

btn = Button(win, command=convert, text='PRESS')
btn.pack(pady=50)

win.mainloop()

内容的提问来源于stack exchange，提问作者Nemanja Gavranovic