f-stringの変数化

下記のようにf-stringを用いて複数の変数を表示するのですが、同じコードを条件分岐などで複数回使います。

print(f"{month:5d} {starting:16.2f} {interest:15.2f} {principal:16.2f} {monthly_payment:7.2f} {remaining:14.2f}")

長く読みづらいので"formatted_output"として定義して再利用できないかと試してみたのですが、どのような形でprintに入れても上手くいきません。

formatted_output = f"{month:5d} {starting:16.2f} {interest:15.2f} {principal:16.2f} {monthly_payment:7.2f} {remaining:14.2f}"

# 上手くいかず
# print(formatted_output)
# print(f"formatted_output")
# print(f"{formatted_output}")

f-stringのコードを変数として定義することはできないのでしょうか?

追記

プログラムは、リボ払いでの各月の金利や支払額を表のように出力するものです。
month, startingなどはprintするごとに変化します。

# Compute a payment schedule

DISCOUNT_RATE = 0.1
ANNUAL_INTEREST_RATE = 0.12
MONTHLY_INTEREST_RATE = ANNUAL_INTEREST_RATE / 12
MONTHLY_PAYMENT_RATE = 0.05

original_price = float(input("Enter the purchase price: "))
discounted_price = original_price * (1 - DISCOUNT_RATE)  # The price for members

month = 1

starting = discounted_price  # The current total balance owed
monthly_payment = (
    discounted_price * MONTHLY_PAYMENT_RATE
)  # the sum of interest and principal for that manth
interest = discounted_price * MONTHLY_INTEREST_RATE
principal = monthly_payment - interest
remaining = starting - principal  # The balance remaining after payment


# display the titles of a table
print(
    "\n"
    "Month  Starting Balance  Interest to Pay  Principal to Pay  Payment  Ending Balance\n"
    "-----------------------------------------------------------------------------------"
)


# Display the info of the first month
print(
    f"{month:5d}  {starting:16.2f}  {interest:15.2f}  {principal:16.2f}  {monthly_payment:7.2f}  {remaining:14.2f}"
)


# Display the info of the second month and later
while monthly_payment <= remaining:
    month += 1
    starting = remaining
    interest = starting * MONTHLY_INTEREST_RATE
    principal = monthly_payment - interest
    remaining = starting - principal

    print(
        f"{month:5d}  {starting:16.2f}  {interest:15.2f}  {principal:16.2f}  {monthly_payment:7.2f}  {remaining:14.2f}"
    )


# Evaluate the remaining and display the info of the last month
if monthly_payment >= remaining:
    month += 1
    starting = remaining
    interest = 0
    principal = starting
    monthly_payment = starting
    remaining = 0

    print(
        f"{month:5d}  {starting:16.2f}  {interest:15.2f}  {principal:16.2f}  {monthly_payment:7.2f}  {remaining:14.2f}"
    )

行動規範の内容に同意します

回答1件

ベストアンサー

f-stringは即時評価されてしまうので、

python
1s = "{month:5d} {starting:16.2f} {interest:15.2f} {principal:16.2f} {monthly_payment:7.2f} {remaining:14.2f}"
2
3print(s.format(month=...))

というように、テンプレートとしての文字列sを一個作って、あとから必要な場所で.formatメソッドを呼ぶ形にすればテンプレートsを使いまわすことができます。

追記

print部分を短くするだけなら次のような方法があります。

位置引数を使う場合。

Python
1s = "{:5d} {:16.2f} {:15.2f} {:16.2f} {:7.2f} {:14.2f}"
2
3values = [1, 2.0, 3.0, 4.0, 5.0, 6.0]
4print(s.format(*values))

キーワード引数を利用する場合。

Python
1s = "{month:5d} {starting:16.2f} {interest:15.2f} {principal:16.2f} {monthly_payment:7.2f} {remaining:14.2f}"
2
3kv = {
4    "month": 1,
5    "starting": 2.0,
6    "interest": 3.0,
7    "principal": 4.0,
8    "monthly_payment": 5.0,
9    "remaining": 6.0
10}
11print(s.format(**kv))

キーワード引数を使う場合だと、例えば一つの変数info(dictクラス)に情報を集約しておく、などですかね。

Python
1# Compute a payment schedule
2
3DISCOUNT_RATE = 0.1
4ANNUAL_INTEREST_RATE = 0.12
5MONTHLY_INTEREST_RATE = ANNUAL_INTEREST_RATE / 12
6MONTHLY_PAYMENT_RATE = 0.05
7
8original_price = float(input("Enter the purchase price: "))
9discounted_price = original_price * \
10    (1 - DISCOUNT_RATE)  # The price for members
11
12info = {
13    "month": 1,
14    "starting": discounted_price,  # The current total balance owed
15    # the sum of interest and principal for that manth
16    "monthly_payment": discounted_price * MONTHLY_PAYMENT_RATE,
17    "interest": discounted_price * MONTHLY_INTEREST_RATE,
18}
19info["principal"] = info["monthly_payment"] - info["interest"]
20# The balance remaining after payment
21info["remaining"] = info["starting"] - info["principal"]
22
23# display the titles of a table
24print(
25    "\n"
26    "Month  Starting Balance  Interest to Pay  Principal to Pay  Payment  Ending Balance\n"
27    "-----------------------------------------------------------------------------------"
28)
29
30
31# Display the info of the first month
32s = "{month:5d}  {starting:16.2f}  {interest:15.2f}  {principal:16.2f}  {monthly_payment:7.2f}  {remaining:14.2f}"
33print(s.format(**info))
34
35
36# Display the info of the second month and later
37while info["monthly_payment"] <= info["remaining"]:
38    info["month"] += 1
39    info["starting"] = info["remaining"]
40    info["interest"] = info["starting"] * MONTHLY_INTEREST_RATE
41    info["principal"] = info["monthly_payment"] - info["interest"]
42    info["remaining"] = info["starting"] - info["principal"]
43
44    print(s.format(**info))
45