Python: 從兩個時間字串開始：用 timedelta 計算時間差，並學會分辨屬性與方法兩種做法; from datetime import datetime

by 儲蓄保險王 · 2025-09-14

目標

以兩個 datetime 字串為起點
解析成 datetime 物件
計算時間差與秒數、分鐘數
展示「屬性派」與「方法派」都能完成相同任務
補充如何正確分辨屬性與方法

先從時間字串開始

start_datetime_str = "2024-02-15 09:18:38.1234"
end_datetime_str   = "2024-02-15 09:20:38.1234"

start_datetime_str = "2024-02-15 09:18:38.1234"
end_datetime_str   = "2024-02-15 09:20:38.1234"

解析成 datetime

from datetime import datetime

fmt = "%Y-%m-%d %H:%M:%S.%f"
start_dt = datetime.strptime(start_datetime_str, fmt)
end_dt   = datetime.strptime(end_datetime_str,   fmt)

print(start_dt)
print(end_dt)

from datetime import datetime

fmt = "%Y-%m-%d %H:%M:%S.%f"
start_dt = datetime.strptime(start_datetime_str, fmt)
end_dt   = datetime.strptime(end_datetime_str,   fmt)

print(start_dt)
print(end_dt)

計算時間差：得到 timedelta

delta = end_dt - start_dt
print(delta)           # 0:02:00
print(type(delta))     # <class 'datetime.timedelta'>

delta = end_dt - start_dt
print(delta)           # 0:02:00
print(type(delta))     # <class 'datetime.timedelta'>

輸出結果:

Python: 從兩個時間字串開始：用 timedelta 計算時間差，並學會分辨屬性與方法兩種做法; from datetime import datetime - 儲蓄保險王

dir()可以列出物件的所有屬性/方法,
但無法區分那一個是屬性,那一個是方法

dir(delta)
"""
['__abs__',
 '__add__',
 '__bool__',
 '__class__',
 '__delattr__',
 '__dir__',
 '__divmod__',
 '__doc__',
 '__eq__',
 '__floordiv__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getstate__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__le__',
 '__lt__',
 '__mod__',
 '__mul__',
 '__ne__',
 '__neg__',
 '__new__',
 '__pos__',
 '__radd__',
 '__rdivmod__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__rfloordiv__',
 '__rmod__',
 '__rmul__',
 '__rsub__',
 '__rtruediv__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__sub__',
 '__subclasshook__',
 '__truediv__',
 'days',
 'max',
 'microseconds',
 'min',
 'resolution',
 'seconds',
 'total_seconds']
"""

dir(delta)
"""
['__abs__',
 '__add__',
 '__bool__',
 '__class__',
 '__delattr__',
 '__dir__',
 '__divmod__',
 '__doc__',
 '__eq__',
 '__floordiv__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getstate__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__le__',
 '__lt__',
 '__mod__',
 '__mul__',
 '__ne__',
 '__neg__',
 '__new__',
 '__pos__',
 '__radd__',
 '__rdivmod__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__rfloordiv__',
 '__rmod__',
 '__rmul__',
 '__rsub__',
 '__rtruediv__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__sub__',
 '__subclasshook__',
 '__truediv__',
 'days',
 'max',
 'microseconds',
 'min',
 'resolution',
 'seconds',
 'total_seconds']
"""

屬性派：用屬性讀數值
timedelta 內建三個主要資料屬性（不需括號）：

days
seconds
microseconds

# 屬性派
minutes_via_attrs = (delta.days * 24 * 3600 + delta.seconds + delta.microseconds/1_000_000) / 60
seconds_via_attrs = delta.days * 24 * 3600 + delta.seconds + delta.microseconds/1_000_000

print(minutes_via_attrs)  # 2.0
print(seconds_via_attrs)  # 120.0

# 屬性派
minutes_via_attrs = (delta.days * 24 * 3600 + delta.seconds + delta.microseconds/1_000_000) / 60
seconds_via_attrs = delta.days * 24 * 3600 + delta.seconds + delta.microseconds/1_000_000

print(minutes_via_attrs)  # 2.0
print(seconds_via_attrs)  # 120.0

說明

timedelta 的內部以天、秒、微秒三部分表達；自行組合就能得出任意單位。
優點：不依賴額外方法，邏輯透明。
缺點：容易手誤，重複性高。

方法派：用方法拿總秒數
timedelta 提供方法 total_seconds()，直接回傳整體秒數（含小數）。

# 方法派
seconds_via_method = delta.total_seconds()
minutes_via_method = seconds_via_method / 60

print(seconds_via_method)  # 120.0
print(minutes_via_method)  # 2.0

# 方法派
seconds_via_method = delta.total_seconds()
minutes_via_method = seconds_via_method / 60

print(seconds_via_method)  # 120.0
print(minutes_via_method)  # 2.0

說明

優點：簡潔、可讀性高。
缺點：依賴該方法存在；若是自訂類型需自行實作。

兩派結果一致性檢查

assert abs(seconds_via_attrs - seconds_via_method) < 1e-9
assert abs(minutes_via_attrs - minutes_via_method) < 1e-9
print("屬性派與方法派的結果一致。")

assert abs(seconds_via_attrs - seconds_via_method) < 1e-9
assert abs(minutes_via_attrs - minutes_via_method) < 1e-9
print("屬性派與方法派的結果一致。")

如何分辨屬性與方法（正確方式）

是否可呼叫：callable(x)
函式/方法判斷：用 inspect，而不是看字串
- inspect.isfunction(x) → 純 Python 函式
- inspect.ismethod(x) → 綁定方法
- inspect.isbuiltin(x) → 內建（C 實作）函式/方法
- 對於類別層的成員，還可用 inspect.ismethoddescriptor(x)

實作範例：觀察 timedelta 成員

import inspect

obj = delta   # 任何物件皆可

attrs = []
methods = []

for name in dir(obj):
    member = getattr(obj, name)
    if callable(member):
        methods.append(name)
    else:
        attrs.append(name)

print("屬性例子：", [n for n in attrs if n in ("days","seconds","microseconds","min","max","resolution")])
print("方法例子：", [n for n in methods if n in ("total_seconds","__add__","__sub__")])

# 進一步看 total_seconds 的型態特性
m = getattr(obj, "total_seconds")
print("callable:", callable(m))
print("ismethod:", inspect.ismethod(m))
print("isfunction:", inspect.isfunction(m))
print("isbuiltin:", inspect.isbuiltin(m))

import inspect

obj = delta   # 任何物件皆可

attrs = []
methods = []

for name in dir(obj):
    member = getattr(obj, name)
    if callable(member):
        methods.append(name)
    else:
        attrs.append(name)

print("屬性例子：", [n for n in attrs if n in ("days","seconds","microseconds","min","max","resolution")])
print("方法例子：", [n for n in methods if n in ("total_seconds","__add__","__sub__")])

# 進一步看 total_seconds 的型態特性
m = getattr(obj, "total_seconds")
print("callable:", callable(m))
print("ismethod:", inspect.ismethod(m))
print("isfunction:", inspect.isfunction(m))
print("isbuiltin:", inspect.isbuiltin(m))