beginner's python help

[Maggie]

code practice:

test = open ("test.txt", "r")
readData = test.readlines()
#set up a sum
sum = 0;
for item in readData:
sum += int(item)
print sum

test file looks something like this:

34
23
124
432
12

when i am trying to compile this it gives me the error: invalid
literal for int() with base 10

i know a lot of people get this and it usually means that you try to
cast a string into an integer and this string does not really contain
a “digit”..so I am just not sure how to correct it in this case...

thanks for your input

 

[Chris Rebert]

code practice:

test = open ("test.txt", "r")
readData = test.readlines()
#set up a sum
sum = 0;
for item in readData:
       sum += int(item)
print sum

A slightly better way to write this:

test = open("test.txt", "r")
#set up a sum
the_sum = 0 #avoid shadowing the built-in function sum()
for line in test: #iterate over the file directly instead of reading
it into a list
the_sum += int(line)
print the_sum

test file looks something like this:

34
23
124
432
12

when i am trying to compile

No, the error is happening at runtime. Pretty much only SyntaxErrors
occur at compile-time.

this it gives me the error: invalid
literal for int() with base 10

i know a lot of people get this and it usually means that you try to
cast a string into an integer and this string does not really contain
a “digitâ€..so I am just not sure how to correct it in this case...

I would recommend putting a `print repr(line)` inside the loop, before
the "+=" line. This will show the input int() is getting so you can
see out what the bad input is that's causing the error and thus debug
the problem.

Cheers,
Chris

 

[Terry Reedy]

code practice:

test = open ("test.txt", "r")
readData = test.readlines()
#set up a sum
sum = 0;
for item in readData:
sum += int(item)
print sum

test file looks something like this:

34
23
124
432
12

when i am trying to compile this it gives me the error: invalid
literal for int() with base 10

i know a lot of people get this and it usually means that you try to
cast a string into an integer and this string does not really contain
a “digit”..so I am just not sure how to correct it in this case...

You already have your specific answer, but you need a general strategy
also. When you have a problem processing data from a file, you should
ask: "Is the problem with the file data? Or is it with the subsequent
processing?". The answers come from two different test programs.

For the first:

print readData
#or
for item in readData: print repr(item)

This would have shown you that the file is not what you thought.

For the second:

readData = ['34', '23'] # etc
#read of program

and it that works, add '\n' to the end of each item.

Any decent programming editor will let you comment out blocks of text
without deleting them.

In other words, to debug, run simple experiments.

Terry Jan Reedy

 

[Esmail]

code practice:

test = open ("test.txt", "r")
readData = test.readlines()
#set up a sum
sum = 0;

Hi Maggie,

I see you have already gotten a lot of useful help.
One additional suggestion would be to use a different
variable name other than 'sum' as sum is a Python
built-in function.

Cheers,
Esmail

 

[Niklas Norrthon]

code practice:

test = open ("test.txt", "r")
readData = test.readlines()
#set up a sum
sum = 0;
for item in readData:
        sum += int(item)
print sum

test file looks something like this:

34
23
124
432
12

Assuming the test file looks like above, and isn't stored in rtf
format or something like that. (Open the test file in the python
editor to check its contents).

/Niklas