Converting list items from string to int(Python)

Question

I have a list:

Student_Grades = ['56', '49', '63']

and I want to convert each of the entries to integers so that I can calculate an average.

Here's my code for converting:

for i in Student_Grades:
    Student_Grades = [int(i)]

I keep getting the error

invalid literal for int() with base 10: '56,'

and I don't know what to do.

Here is my full code on how I got Student_Grades Choose_File = str(input("Please enter the exact name of the file to be read in (including file extention) : "))

with open(Choose_File, "r") as datafile:
    counter = 1
    x = 1
    Student_Grades = []
    Read = datafile.readlines()
    info = Read[counter]
    Split_info = info.split()
    n = len(Split_info)


    while x < n:
        Student_Grades.append(Split_info[x])
        x = x + 2

The textfile has the format 'MECN1234 56, MECN1357 49, MATH1111 63'

Solution 1

You should do this:

for i in range(len(Student_Grades)):
    Student_Grades[i] = int(Student_Grades[i])

Solution 2

Apply int on each item in the list and return it as a list:

>>> StudentGrades = ['56', '49', '63']
>>> res = list(map(int, StudentGrades)) # this call works for Python 2.x as well as for 3.x
>>> print res
[56, 49, 63]

Note about map differences in Python 2 and 3

In Python 2.x map returns directly the list, so you may use

>>> res = map(int, StudentGrades)

but in Python 3.x map returns an iterator, so to get real list, it must be wrapped into list call:

>>> res = list(map(int, StudentGrades))

The later way works well in both version of Python

Solution 3

In [7]:

Student_Grades = ['56', '49', '63']
new_list = [int(i) for i in Student_Grades]
print(new_list)
[56, 49, 63]

Comments

[Benjamin Bannier]

I think she wants to update the list.

[Quintec]

@BenjaminBannier Yes, I changed it.

[swami_108]

This returned <map object at 0x00000000032BD518> and I'm not quite sure what this means. Forgive me, I'm new to programming

[askewchan]

@user3576929, you must be using Python 3 and @Jan is using python 2. You can fix this by using list(map(int, StudentGrades))

[Jan Vlcinsky]

@askewchan Thanks for your comment, I updated my answer to be Python 2 and 3 compatible