Why does the invalid syntax error occur?

Question

Python

I'm writing api, I can't understand what's the matter here. What did I do wrong?

def generate_rec_structures(currency, exp, lang):
    s_path = os.path.dirname(os.path.realpath(__file__))
    file_path = s_path + '/data.pickle'
    with open(file_path, 'rb') as f:
        data = pickle.load(f)
        
    board = data[currency]
    df = pd.DataFrame(board)
    df = df.loc[df['instrument_name'].apply(lambda x: len(x.split('-'))) == 4]
    df['exp'] = df['instrument_name'].apply(lambda x: x.split('-')[1])
    
    df_tmp = df.loc[df['exp'] == exp]        
    df_tmp['strike'] = df_tmp['instrument_name'].apply(lambda x: x.split('-')[2])
    strike_list = df_tmp['strike'].unique()
    strike_list = [int(i) for i in strike_list]
    strike_list = sorted(strike_list)
    price = df_tmp['estimated_delivery_price'].mean()

    data = []

    strike_0 = utils.find_nearest(strike_list, price * 1.02)
    strike_1 = utils.find_nearest(strike_list, price * 1.15)
    if strike_0 == strike_1:
        ind = strike_list.index(strike_1) + 1
        if ind != len(strike_list):
            strike_1 = strike_list[ind]
    strike_0_str = str(int(strike_0))
    strike_1_str = str(int(strike_1))
    diff_str = str(int(strike_1 - strike_0))
    
    if lang = 'ru':
        description = "Если цена {3} при погашении выше {0} USD и ниже {1} USD, то инвестор получает дополнительный доход 1:1 отражающий рост {3}. Если цена {3} при погашении ниже {0} USD, то опционная составляющая оказывается вне денег, что эквивалентно 0% дополнительного дохода. Если цена {3} при погашении выше {1} USD, то дополнительный доход ограничен на уровне {2} USD (что эквивалентно {1} USD – {0} USD)".format(strike_0_str, strike_1_str, diff_str, currency)
    else:
        description = "If the price of {3} at maturity is above {0} USD and below {1} USD, then the investor receives an additional 1:1 income reflecting the growth of {3}. If the {3} price at maturity is below {0} USD, then the option component is out of the money, which is equivalent to 0% additional income. If the price of {3} at maturity is higher than {1} USD, then the additional income is capped at {2} USD (which is equivalent to {1} USD - {0} USD)".format(strike_0_str, strike_1_str, diff_str, currency)
    
    data.append({
        "structure":[
            {
                "instrument name":None,
                "type":"call",
                "direction":1,
                "strike":strike_0,
                "amount":1
            },
            {
                "instrument name":None,
                "type":"call",
                "direction":-1,
                "strike":strike_1,
                "amount":1
            }
        ],
        "description":description,
        "title":"Call-spread"
    })

Mistake

Traceback (most recent call last):
  File "C:\Users\Vladik\Desktop\calculator_api (v-1.3)\main.py", line 10, in <module>
    import structs
  File "C:\Users\Vladik\Desktop\calculator_api (v-1.3)\structs.py", line 170
    if lang = 'ru':
            ^
SyntaxError: invalid syntax

Answer 1

Well, the check seems to be done through ==