What does square bracket means in xlabel - Mission 145

Q&A DQ Courses
#1

Hi in Mission 145 https://app.dataquest.io/m/145/histograms-and-box-plots/8/multiple-box-plots, i have a question.

I used square bracket in the ax.set_xticklabels([num_cols],rotation = 90) and it ends up setting the labels all in 1 line. Am afraid i am still confused on when to use square bracket or when not to use square brackets when working with charts

num_cols = ['RT_user_norm', 'Metacritic_user_nom', 'IMDB_norm', 'Fandango_Ratingvalue']

fig, ax = plt.subplots()

ax.boxplot(norm_reviews[num_cols].values)
ax.set_xticklabels([num_cols],rotation = 90)

ax.set_ylim(0,5)

plt.show()

i do realize the right answer is by removing the square bracket, but wants to know when should i use square bracket and when not to

#2

Answering my own question here as again stuck with the same problem during the problem in Regex
https://app.dataquest.io/m/354/regular-expression-basics/5/quantifiers

I used this

email_titles = titles.str.contains(email_bool)

where it triggers the error

> 'Series' objects are mutable, thus they cannot be hashed

However, when changed to the answer guide given

email_titles = titles[email_bool]

When googling, found this in Stackexchange

Hope it helps others whom may make the silly mistake like me

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