Why does  appear in my data?

I downloaded the file 'pi_million_digits.txt' from here:

https://github.com/ehmatthes/pcc/blob/master/chapter_10/pi_million_digits.txt

I then used this code to open and read it:

filename = 'pi_million_digits.txt'

with open(filename) as file_object:
    lines = file_object.readlines()

pi_string = ''
for line in lines:
    pi_string += line.strip()

print(pi_string[:52] + "...")
print(len(pi_string))

However the output produced is correct apart from the fact it is preceded by same strange symbols: "3.141...."

What causes these strange symbols? I am stripping the lines so I'd expect such symbols to be removed.