Python Datetime：Pythonの日付と時刻の完全ガイド

from datetime import datetime, date
 
# 現在の日付と時刻
now = datetime.now()
print(now)           # 2026-02-10 14:30:45.123456
 
# 現在の日付のみ
today = date.today()
print(today)         # 2026-02-10
 
# datetime.today()はdatetime.now()に似ていますが、タイムゾーンサポートなし
now_alt = datetime.today()
print(now_alt)       # 2026-02-10 14:30:45.123456

from datetime import datetime
from zoneinfo import ZoneInfo
 
# タイムゾーン対応の現在時刻
utc_now = datetime.now(tz=ZoneInfo("UTC"))
print(utc_now)  # 2026-02-10 14:30:45.123456+00:00
 
tokyo_now = datetime.now(tz=ZoneInfo("Asia/Tokyo"))
print(tokyo_now)  # 2026-02-10 23:30:45.123456+09:00

from datetime import datetime, date, time
 
# 年、月、日、時、分、秒から
dt = datetime(2026, 3, 15, 9, 30, 0)
print(dt)  # 2026-03-15 09:30:00
 
# 日付のみ
d = date(2026, 12, 25)
print(d)  # 2026-12-25
 
# 時刻のみ
t = time(14, 30, 0)
print(t)  # 14:30:00
 
# 日付と時刻を結合
combined = datetime.combine(d, t)
print(combined)  # 2026-12-25 14:30:00

from datetime import datetime
 
dt = datetime(2026, 3, 15, 9, 30, 45)
 
print(dt.year)        # 2026
print(dt.month)       # 3
print(dt.day)         # 15
print(dt.hour)        # 9
print(dt.minute)      # 30
print(dt.second)      # 45
print(dt.weekday())   # 6 (日曜日、月曜日=0)
print(dt.isoformat()) # 2026-03-15T09:30:45

from datetime import datetime
 
dt = datetime(2026, 3, 15, 9, 5, 7)
 
# 一般的なフォーマット
print(dt.strftime("%Y-%m-%d"))              # 2026-03-15
print(dt.strftime("%d/%m/%Y"))              # 15/03/2026
print(dt.strftime("%B %d, %Y"))             # March 15, 2026
print(dt.strftime("%Y-%m-%d %H:%M:%S"))     # 2026-03-15 09:05:07
print(dt.strftime("%I:%M %p"))              # 09:05 AM
print(dt.strftime("%A, %B %d, %Y"))         # Sunday, March 15, 2026

from datetime import datetime
 
# さまざまな日付文字列フォーマットをパース
dt1 = datetime.strptime("2026-03-15", "%Y-%m-%d")
print(dt1)  # 2026-03-15 00:00:00
 
dt2 = datetime.strptime("15/03/2026", "%d/%m/%Y")
print(dt2)  # 2026-03-15 00:00:00
 
dt3 = datetime.strptime("March 15, 2026 09:30 AM", "%B %d, %Y %I:%M %p")
print(dt3)  # 2026-03-15 09:30:00
 
dt4 = datetime.strptime("2026-03-15T09:30:00", "%Y-%m-%dT%H:%M:%S")
print(dt4)  # 2026-03-15 09:30:00

from datetime import datetime
 
def safe_parse_date(date_string, fmt="%Y-%m-%d"):
    """Parse a date string safely, returning None on failure."""
    try:
        return datetime.strptime(date_string, fmt)
    except ValueError as e:
        print(f"Could not parse '{date_string}': {e}")
        return None
 
# Valid input
print(safe_parse_date("2026-03-15"))       # 2026-03-15 00:00:00
 
# Invalid input
print(safe_parse_date("15-03-2026"))       # Could not parse '15-03-2026': ...
print(safe_parse_date("not a date"))       # Could not parse 'not a date': ...

from datetime import datetime
 
def parse_flexible_date(date_string):
    """Try multiple date formats and return the first match."""
    formats = [
        "%Y-%m-%d",
        "%d/%m/%Y",
        "%m/%d/%Y",
        "%B %d, %Y",
        "%b %d, %Y",
        "%Y-%m-%dT%H:%M:%S",
        "%Y-%m-%d %H:%M:%S",
    ]
    for fmt in formats:
        try:
            return datetime.strptime(date_string, fmt)
        except ValueError:
            continue
    raise ValueError(f"No matching format found for '{date_string}'")
 
print(parse_flexible_date("2026-03-15"))         # 2026-03-15 00:00:00
print(parse_flexible_date("March 15, 2026"))     # 2026-03-15 00:00:00
print(parse_flexible_date("15/03/2026"))         # 2026-03-15 00:00:00

from datetime import datetime, timedelta
 
now = datetime(2026, 2, 10, 12, 0, 0)
 
# 日数を加算
tomorrow = now + timedelta(days=1)
print(tomorrow)  # 2026-02-11 12:00:00
 
# 日数を減算
last_week = now - timedelta(weeks=1)
print(last_week)  # 2026-02-03 12:00:00
 
# 時間と分を加算
later = now + timedelta(hours=5, minutes=30)
print(later)  # 2026-02-10 17:30:00
 
# 複数の単位を組み合わせる
future = now + timedelta(weeks=2, days=3, hours=6)
print(future)  # 2026-02-27 18:00:00

from datetime import datetime
 
start = datetime(2026, 1, 1)
end = datetime(2026, 12, 31)
 
diff = end - start
print(diff)              # 364 days, 0:00:00
print(diff.days)         # 364
print(diff.total_seconds())  # 31449600.0

from datetime import timedelta
 
delta = timedelta(weeks=1, days=2, hours=3, minutes=30, seconds=45)
print(delta)                    # 9 days, 3:30:45
print(delta.days)               # 9
print(delta.seconds)            # 12645 (3*3600 + 30*60 + 45)
print(delta.total_seconds())    # 790245.0

from datetime import datetime
 
dt1 = datetime(2026, 1, 1)
dt2 = datetime(2026, 6, 15)
dt3 = datetime(2026, 12, 31)
 
print(dt1 < dt2)    # True
print(dt3 > dt2)    # True
print(dt1 == dt2)   # False
print(dt1 != dt2)   # True

from datetime import datetime
 
dates = [
    datetime(2026, 12, 25),
    datetime(2026, 1, 1),
    datetime(2026, 7, 4),
    datetime(2026, 2, 14),
]
 
sorted_dates = sorted(dates)
for d in sorted_dates:
    print(d.strftime("%B %d, %Y"))
 
# January 01, 2026
# February 14, 2026
# July 04, 2026
# December 25, 2026

from datetime import datetime, timezone
 
# Datetimeからタイムスタンプへ
dt = datetime(2026, 3, 15, 9, 30, 0)
ts = dt.timestamp()
print(ts)  # 1773814200.0 (ローカルタイムゾーンに依存)
 
# タイムスタンプからDatetimeへ（タイムゾーン対応、推奨）
dt_aware = datetime.fromtimestamp(ts, tz=timezone.utc)
print(dt_aware)  # 2026-03-15 01:30:00+00:00

from datetime import datetime, timezone, timedelta
 
# UTC
utc_now = datetime.now(timezone.utc)
print(utc_now)  # 2026-02-10 14:30:00+00:00
 
# 固定オフセット（例：インドのUTC+5:30）
ist = timezone(timedelta(hours=5, minutes=30))
india_time = datetime.now(ist)
print(india_time)  # 2026-02-10 20:00:00+05:30
 
# タイムゾーン間の変換
utc_time = datetime(2026, 3, 15, 12, 0, 0, tzinfo=timezone.utc)
eastern = timezone(timedelta(hours=-5))
eastern_time = utc_time.astimezone(eastern)
print(eastern_time)  # 2026-03-15 07:00:00-05:00

from datetime import datetime
from zoneinfo import ZoneInfo
 
# 名前付きタイムゾーン
utc = ZoneInfo("UTC")
eastern = ZoneInfo("America/New_York")
tokyo = ZoneInfo("Asia/Tokyo")
 
# タイムゾーン対応のdatetimeを作成
dt = datetime(2026, 7, 15, 12, 0, 0, tzinfo=utc)
print(dt)  # 2026-07-15 12:00:00+00:00
 
# 他のタイムゾーンに変換
print(dt.astimezone(eastern))  # 2026-07-15 08:00:00-04:00 (EDT)
print(dt.astimezone(tokyo))    # 2026-07-15 21:00:00+09:00

from datetime import date
 
def calculate_age(birth_date):
    """Calculate age in years from a birth date."""
    today = date.today()
    age = today.year - birth_date.year
    if (today.month, today.day) < (birth_date.month, birth_date.day):
        age -= 1
    return age
 
birthday = date(1995, 8, 20)
print(f"Age: {calculate_age(birthday)} years")  # Age: 30 years (as of Feb 2026)

from datetime import date, timedelta
 
def date_range(start, end, step_days=1):
    """Generate dates from start to end (inclusive)."""
    current = start
    while current <= end:
        yield current
        current += timedelta(days=step_days)
 
start = date(2026, 2, 1)
end = date(2026, 2, 7)
 
for d in date_range(start, end):
    print(d.strftime("%A, %B %d"))

from datetime import date, timedelta
 
def business_days_between(start, end):
    """Count weekdays (Mon-Fri) between two dates, excluding endpoints."""
    count = 0
    current = start + timedelta(days=1)
    while current < end:
        if current.weekday() < 5:  # 0=Mon, 4=Fri
            count += 1
        current += timedelta(days=1)
    return count
 
start = date(2026, 2, 1)
end = date(2026, 2, 28)
print(f"Business days: {business_days_between(start, end)}")  # Business days: 19

from datetime import datetime
 
# strftime: datetime -> string
dt = datetime(2026, 3, 15, 9, 30)
formatted = dt.strftime("%B %d, %Y at %I:%M %p")
print(formatted)  # March 15, 2026 at 09:30 AM
 
# strptime: string -> datetime
parsed = datetime.strptime("March 15, 2026 at 09:30 AM", "%B %d, %Y at %I:%M %p")
print(parsed)  # 2026-03-15 09:30:00