Error with for loop

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#1

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My Code:

index = 0
for row in data:
    data[index] = row[:-1]
    index =+ 1

print(data[:3])

What I expected to happen:
[[‘August 19, 1971’, ‘Santa Martha Acatitla’, ‘Mexico’, ‘Yes’], [‘September 25, 2020’, ‘Forest prison, Brussels’, ‘Belgium’, ‘No’, ‘Kristel A.’], [‘May 24, 1978’, ‘United States Penitentiary, Marion’, ‘United States’, ‘No’, ‘Garrett Brock TrapnellMartin Joseph McNallyJames Kenneth Johnson’]]

What actually happened:

[['August 19, 1971', 'Santa Martha Acatitla', 'Mexico', 'Yes'], ['September 25, 2020', 'Forest prison, Brussels', 'Belgium', 'No', 'Kristel A.'], ['May 24, 1978', 'United States Penitentiary, Marion', 'United States', 'No', 'Garrett Brock TrapnellMartin Joseph McNallyJames Kenneth Johnson', "43-year-old Barbara Ann Oswald hijacked a Saint Louis-based charter helicopter and forced the pilot to land in the yard at USP Marion. While landing the aircraft, the pilot, Allen Barklage, who was a Vietnam War veteran, struggled with Oswald and managed to wrestle the gun away from her. Barklage then shot and killed Oswald, thwarting the escape.[10] A few months later Oswald's daughter hijacked TWA Flight 541 in an effort to free Trapnell."]]

Other details:

The first two elements are correct i.e. the details column has been removed. However, in the third row, the details column remains. I am confused if the code worked for the first two iterations, why didn’t it work for the 3rd time?

#2

This is the source of the problem and can be easy to miss.

a += 1 is the same as a = a + 1. However, a =+ 1 is the same as a = (+1).

You are setting the index to 1 for every iteration.

Your first two elements in the output are not correct either, as a result. You get -

instead of

['August 19, 1971', 'Santa Martha Acatitla', 'Mexico', 'Yes', 'Joel David Kaplan Carlos Antonio Contreras Castro']

and

instead of

['October 31, 1973', 'Mountjoy Jail', 'Ireland', 'Yes', "JB O'Hagan Seamus TwomeyKevin Mallon"]

Once you fix your index update step and re-run the entire code, you should see the correct output.

2 Likes
#3

Thank you so much for the detailed reply! That was very helpful.