I have an error on line 34. Please help I am not sure how to define this at the beginning of the code to run properly.

Here is the error, NameError: name 'assigned_team_df' is not defined

# Write your code in this code block section
import pandas as pd
import scipy.stats as st
st.norm.interval(0.95, mean, stderr)
# Mean relative skill of assigned teams from the years 1996-1998
#importing the file
assigned_years_league_df = pd.read_csv('nbaallelo.csv')

mean = assigned_years_league_df['elo_n'].mean()

# Standard deviation of the relative skill of all teams from the years 1996-1998
stdev = assigned_years_league_df['elo_n'].std()

n = len(assigned_years_league_df)

#Confidence interval
stderr = stdev/(n ** 0.5) # variable stdev is the calculated the standard deviation of the relative skill of all teams from the years 2013-2015
# ---- TODO: make your edits here ----
# Calculate the confidence interval
# Confidence level is 95% => 0.95
# variable mean is the calculated the mean relative skill of all teams from the years 1996-1998
# variable stderr is the calculated the standard error

conf_int_95 = st.norm.interval(0.95, mean, stderr)

print("95% confidence interval (unrounded) for Average Relative Skill (ELO) in the years 1996 to 1998 =", conf_int_95)
print("95% confidence interval (rounded) for Average Relative Skill (ELO) in the years 1996 to 1998 = (", round(conf_int_95[0], 2),",", round(conf_int_95[1], 2),")")


print("\n")
print("Probability a team has Average Relative Skill LESS than the Average Relative Skill (ELO) of Bulls in the years 1996 to 1998")
print("----------------------------------------------------------------------------------------------------------------------------------------------------------")

mean_elo_assigned_team = assigned_team_df['elo_n'].mean()

choice1 = st.norm.sf(mean_elo_assigned_team, mean, stdev)
choice2 = st.norm.cdf(mean_elo_assigned_team, mean, stdev)

# Pick the correct answer.
print("Which of the two choices is correct?")
print("Choice 1 =", round(choice1,4))
print("Choice 2 =", round(choice2,4))

95% confidence interval (unrounded) for Average Relative Skill (ELO) in the years 1996 to 1998 = (1494.6158622635041, 1495.8562484985657)
95% confidence interval (rounded) for Average Relative Skill (ELO) in the years 1996 to 1998 = ( 1494.62 , 1495.86 )


Probability a team has Average Relative Skill LESS than the Average Relative Skill (ELO) of Bulls in the years 1996 to 1998
----------------------------------------------------------------------------------------------------------------------------------------------------------

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NameError Traceback (most recent call last)
in
32 print("----------------------------------------------------------------------------------------------------------------------------------------------------------")
33
---> 34 mean_elo_assigned_team = assigned_team_df['elo_n'].mean()
35
36 choice1 = st.norm.sf(mean_elo_assigned_team, mean, stdev)

NameError: name 'assigned_team_df' is not defined