如何通过python打开文件

Question

I am very new to programming and the python language.

I know how to open a file in python, but the question is how can I open the file as a parameter of a function?

example:

function(parameter)

Here is how I have written out the code:

def function(file):
    with open('file.txt', 'r') as f:
        contents = f.readlines()
    lines = []
    for line in f:
        lines.append(line)
    print(contents)    

Answer 1

You can easily pass the file object.

with open('file.txt', 'r') as f: #open the file
    contents = function(f) #put the lines to a variable.

and in your function, return the list of lines

def function(file):
    lines = []
    for line in f:
        lines.append(line)
    return lines 

Another trick, python file objects actually have a method to read the lines of the file. Like this:

with open('file.txt', 'r') as f: #open the file
    contents = f.readlines() #put the lines to a variable (list).

With the second method, readlines is like your function. You don't have to call it again.

Update Here is how you should write your code:

First method:

def function(file):
    lines = []
    for line in f:
        lines.append(line)
    return lines 
with open('file.txt', 'r') as f: #open the file
    contents = function(f) #put the lines to a variable (list).
    print(contents)

Second one:

with open('file.txt', 'r') as f: #open the file
    contents = f.readlines() #put the lines to a variable (list).
    print(contents)

Hope this helps!

Answer 2

Python allows to put multiple open() statements in a single with. You comma-separate them. Your code would then be:

def filter(txt, oldfile, newfile):
    '''\
    Read a list of names from a file line by line into an output file.
    If a line begins with a particular name, insert a string of text
    after the name before appending the line to the output file.
    '''

    with open(newfile, 'w') as outfile, open(oldfile, 'r', encoding='utf-8') as infile:
        for line in infile:
            if line.startswith(txt):
                line = line[0:len(txt)] + ' - Truly a great person!\n'
            outfile.write(line)

# input the name you want to check against
text = input('Please enter the name of a great person: ')    
letsgo = filter(text,'Spanish', 'Spanish2')

And no, you don't gain anything by putting an explicit return at the end of your function. You can use return to exit early, but you had it at the end, and the function will exit without it. (Of course with functions that return a value, you use the return to specify the value to return.)

Answer 3

def fun(file):
    contents = None

    with open(file, 'r') as fp:
        contents = fp.readlines()

    ## if you want to eliminate all blank lines uncomment the next line
    #contents = [line for line in ''.join(contents).splitlines() if line]

    return contents

print fun('test_file.txt')

or you can even modify this, such a way it takes file object as a function arguement as well

Answer 4

Here's a much simpler way of opening a file without defining your own function in Python 3.4:

var=open("A_blank_text_document_you_created","type_of_file")
var.write("what you want to write")
print (var.read()) #this outputs the file contents
var.close() #closing the file

Here are the types of files:

• "r" : just to read a file

• "w" : just to write a file

• "r+" : a special type which allows both reading and writing of the file

For more information see this cheatsheet .

Answer 5

def main():
       file=open("chirag.txt","r")
       for n in file:
              print (n.strip("t"))
       file.close()
if __name__== "__main__":
       main()


the other method is 


with open("chirag.txt","r") as f:
       for n in f:
              print(n)