format文でエラーが発生する

Question

前提・実現したいこと

pythonで数学の計算問題を作りたい

発生している問題・エラーメッセージ

問題・解答を表示するprint_eqとprint_ansを実装中に以下のエラーメッセージが発生しました。
実行すれば必ずエラーが発生するというわけではなく、self.varとself.ans1とself.ans2の型は確認したのですが...

問27：<class 'str'>
{}^2 -{}
Traceback (most recent call last):
  File "calc.py", line 116, in <module>
    tenkai[i-1].print_ans()
  File "C:\---\---\calc\Quadratic.py", line 83, in print_ans
    print("{}^2 -{}").format(self.var, self.var)
AttributeError: 'NoneType' object has no attribute 'format'

該当のソースコード

#-------------解の最大最小の決定
max = 15
min = -15
vars = ["a", "b", "c", "t", "m", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x", "x"]
      

#-------------------以下乗法公式関係----------------------------------------

class tenkai:
    def __init__(self):
        self.var = random.choice(vars)
        b = random.randint(1, 7)

        if b == 1:
            self.ans1 = random.randint(min, max)
            self.ans2 = self.ans1

        elif b == 2:
            self.ans1 = random.randint(min, max)
            self.ans2 = -self.ans1

        else:
            self.ans1 = random.randint(min, max)
            self.ans2 = random.randint(min, max)
   
        if self.ans1 == 0 and self.ans2 == 0:
            a = random.randint(1, 3)
            if a == 1:
                self.ans1 += random.randint(1, max+1)
                self.ans2 = self.ans1
            elif a == 2:
                self.ans1 += -random.randint(1, max+1)
                self.ans2 = self.ans1
            else:
                self.ans1 += random.randint(1, max+1)
                self.ans2 = -self.ans1
        else:
            pass

    def adabs(self, a):
        if a > 0:
            return "+{}".format(str(abs(a)))
        elif a == 0:
            return "+0"
        elif a < 0:
            return "-{}".format(str(abs(a)))
        else:
            pass

    def print_eq(self):
        print(type(self.var))
        if self.ans1 == self.ans2:
            print("({} {})^2".format(self.var, self.adabs(self.ans1)))
        elif self.ans1 == 0:
            print("{}({} {})".format(self.var, self.var, self.adabs(self.ans2)))
        elif self.ans2 == 0:
            print("{}({} {})".format(self.var, self.var, self.adabs(self.ans1)))
        else:
            print("({} {})({} {})".format(self.var, self.adabs(self.ans1), self.var, self.adabs(self.ans2)))

    def print_ans(self):
        print(type(self.var))
        if self.ans1 + self.ans2 == 1 and self.ans1*self.ans2 == 0:
            print("{}^2 +{}").format(self.var, self.var)

        elif self.ans1 + self.ans2 == 1 and self.ans1*self.ans2 != 0:
            print("{}^2 +{} {}".format(self.var, self.var, self.adabs(self.ans1*self.ans2)))

        elif self.ans1 + self.ans2 == -1 and self.ans1*self.ans2 == 0:
            print("{}^2 -{}").format(self.var, self.var)

        elif self.ans1 + self.ans2 == -1 and self.ans1*self.ans2 != 0:
            print("{}^2 -{} {}".format(self.var, self.var, self.adabs(self.ans1*self.ans2)))

        elif self.ans1 + self.ans2 != 1 and self.ans1 + self.ans2 != -1 and self.ans1*self.ans2 == 0:
            print("{}^2 {}{}".format(self.var, self.adabs(self.ans1+self.ans2), self.var))

        elif self.ans1 + self.ans2 == 0 : 
            print("{}^2 {}".format(self.var, self.adabs(self.ans1*self.ans2)))

        else:
            print("{}^2 {}{} {}".format(self.var, self.adabs(self.ans1+self.ans2), self.var, self.adabs(self.ans1*self.ans2)))

試したこと

問題となっているであろうself.varとself.ans1とself.ans2の型は確認しました

Answer 1

print("{}^2 -{}".format(self.var, self.var))

Comments

[syc98]

こんな初歩的なミスだったとは…　精進します。
ありがとうございました！