从txt文件中读取数据

Question

def main():
    file_output=open(r'C:\Users\P\Desktop\randominput.txt','r')

    for num in file_output:
        number=file_output.read()
        print(number)
main()

output:

48
85
58
16
11
82

Actual data in the txt file is

53
48
85
58
16
11
82

Why is my python program not reading the first number??

Answer 1

Use a simple print to trace what's going on:

for num in file_output:
    print("num=", num)
    number=file_output.read()
    print(number)

Output:

num= 53

48
85
58
16
11
82

Note the effect: num is the first input number, but it appears only once. You go through the loop only once.

Your for loop grabs the first number out of the file; the read within the loop grabs the remainder of the file as one input.

I suggest that you look up that actual function of each command you're using; you're not quite clear on the operation yet.

---

REPAIR

def main():
    with open("so.txt") as file_output:

        for num in file_output:
            print("num=", num)
main()

Output:

num= 53

num= 48

num= 85

num= 58

num= 16

num= 11

num= 82

Note that you're still reading these as strings, complete with newline character. Continuing from here is left as an exercise for the reader. :-)

Answer 2

The first line of the file is consumed during the first iteration of the for loop. The read() then reads the file from the current position in the file, which is the beginning of the second line, to the end of the file.

So the print() is printing the contents of the file in one go, having skipped over the first line.

To fix your code:

with open(r'C:\Users\P\Desktop\randominput.txt', 'r') as file_input:
    for number in file_input:
        print(number.rstrip())

The rstrip() is there to remove the new line character at the end of each line. Also the file is opened in a context manager using with . This will ensure that the file will be closed in all circumstances.

Answer 3

is it a typo that in the "open(r'C:\\Users\\P\\Desktop\\randominput.txt','r')" there is an r before 'C\\Users\\P...'? that shouldn't be there.

I believe you are trying to print every number from a text file. here is a way you could do this:

f = open("C:/Users/u/file.txt")
file_contents = f.read()
numbers = str(file_contents).split()
for x in range (0, len(numbers) - 1):
    print (str(numbers[x]))

Answer 4

Your program is reading the first number. When you begin iterating over the file object, for num in file_output: the first line of the file is read, so num is the first number and the file reader is now looking at the second, waiting for the next iteration.

You then call .read() which will read to the end of the file. This gives you all the rest of the numbers in number and moves the reader to the end of the file, terminating the iteration. You want either:

for num in file_output:
    print(num)

or

numbers = file_output.read()
for n in numbers:
    print(n)