将文件作为函数参数传递

Question

If I have a text file ( sequencedata.txt ) in a directory named documents:

/~/documents/sequencedata.txt

How would I define a function named sequenceinfo that would count the number of entries that start with # in the file of above pathway and return this count with the syntax "there are * entries" , in which the * is the counted number of entries?

What I have so far:

#!/usr/bin/python
def sequenceinfo(sequencedata):
    my_file = open("/~/documents/sequencedata.txt")
    my_dna = my_file.read()
    ecoliseq = my_dna.count('#')
    return ecoliseq

print("There are " + str(ecoliseq) + " sequences")

Answer 1

There are a few things here:

1. The name ecoliseq is not visible outside of the function sequenceinfo . Consequentially, the print line will raise a NameError because Python will be unable to find ecoliseq . However, ecoliseq is returned by the function, which means that you can access its value by calling the function and then printing the result.

2. You made sequenceinfo take an argument that is never used. Is this supposed to be the path to the file? I'm going to assume that it is, but you should remove it if not.

3. Not a major problem, but you are not closing the file when you are done with it. You should always manage and properly release the resources that your program aquires. The easiest way to do this with files is to use a with-statement to open them, which will automatically close them for you.

In all, your code should look something like the following:

#!/usr/bin/python
def sequenceinfo(path):
    with open(path) as my_file:
        my_dna = my_file.read()
    ecoliseq = my_dna.count('#')
    return ecoliseq

print("There are " + str(sequenceinfo("/~/documents/sequencedata.txt")) + " sequences")

Also, there may be a fourth problem in that my_dna.count('#') will return the count of every # in the file. But you said in your question that you only want to count the entries that start with # . You will need to fix this bug if so.