What does second last line means ? df['Signal'] = np.nan what does it represent in last line?

Installations & Python Packages
1

import pandas as pd

import numpy as np

import talib as ta

import matplotlib.pyplot as plt

Import Data 

df = pd.read_csv('APPLE.csv',index_col=0)

df = df[['Adj_Open','Adj_High', 'Adj_Low', 'Adj_Close']]

df =df.rename(columns={'Adj_Open': 'Open', 'Adj_High': 'High', 'Adj_Low':'Low', 'Adj_Close':'Close'})

df.index = pd.to_datetime(df.index)

Drop NaN values

df = df.dropna()

Calculate Parabolic SAR

df['SAR']=ta.SAR(df.High.values, df.Low.values, acceleration = 0.02, maximum = 0.2)

Calculate Stochastic Oscillator

df['fastk'], df['fastd'] = ta.STOCHF(df.High.values, df.Low.values, df.Close.values ,fastk_period=5, fastd_period=3)

df['slowk'], df['slowd'] = ta.STOCH(df.High.values, df.Low.values, df.Close.values ,fastk_period=5, slowk_period=3, slowd_period=3)



df['Signal'] = np.nan



df.loc[(df.SAR< df.Close) & (df.fastd>df.slowd) & (df.fastk>df.slowk),'Signal'] = 1

2

In the second last line, we created a column name 'Signal' in dataframe df, which stores NaN values.

In the last line, in the 'Signal' column of dataframe df, we stored 1 when the conditions satisfied. So the purpose of the second last line is to create a column that stores value whenever the condition in the last line meets. However, the second last line is redundant, and you can skip that.