open read and close a file in 1 line of code

Question

Now I use:

pageHeadSectionFile = open(\'pagehead.section.htm\',\'r\')
output = pageHeadSectionFile.read()
pageHeadSectionFile.close()

But t

Answer 1

Python Standard Library Pathlib module does what you looking for:

Path('pagehead.section.htm').read_text()

Don't forget to import Path:

jsk@dev1:~$ python3
Python 3.5.2 (default, Sep 10 2016, 08:21:44)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from pathlib import Path
>>> (Path("/etc") / "hostname").read_text()
'dev1.example\n'

On Python 27 install backported pathlib or pathlib2

Answer 2

Using CPython, your file will be closed immediately after the line is executed, because the file object is immediately garbage collected. There are two drawbacks, though:

1. In Python implementations different from CPython, the file often isn't immediately closed, but rather at a later time, beyond your control.

2. In Python 3.2 or above, this will throw a ResourceWarning, if enabled.

Better to invest one additional line:

with open('pagehead.section.htm','r') as f:
    output = f.read()

This will ensure that the file is correctly closed under all circumstances.

Answer 3

If you want that warm and fuzzy feeling just go with with.

For python 3.6 I ran these two programs under a fresh start of IDLE, giving runtimes of:

0.002000093460083008  Test A
0.0020003318786621094 Test B: with guaranteed close

So not much of a difference.

#--------*---------*---------*---------*---------*---------*---------*---------*
# Desc: Test A for reading a text file line-by-line into a list
#--------*---------*---------*---------*---------*---------*---------*---------*

import sys
import time

#                                  # MAINLINE
if __name__ == '__main__':
    print("OK, starting program...")

    inTextFile = '/Users/Mike/Desktop/garbage.txt'

#                                  # Test: A: no 'with;
    c=[]
    start_time = time.time()
    c = open(inTextFile).read().splitlines()
    print("--- %s seconds ---" % (time.time() - start_time))

    print("OK, program execution has ended.")
    sys.exit()                     # END MAINLINE

OUTPUT:

OK, starting program...
--- 0.002000093460083008 seconds ---
OK, program execution has ended.

#--------*---------*---------*---------*---------*---------*---------*---------*
# Desc: Test B for reading a text file line-by-line into a list
#--------*---------*---------*---------*---------*---------*---------*---------*

import sys
import time

#                                  # MAINLINE
if __name__ == '__main__':
    print("OK, starting program...")

    inTextFile = '/Users/Mike/Desktop/garbage.txt'

#                                  # Test: B: using 'with'
    c=[]
    start_time = time.time()
    with open(inTextFile) as D: c = D.read().splitlines()
    print("--- %s seconds ---" % (time.time() - start_time))

    print("OK, program execution has ended.")
    sys.exit()                     # END MAINLINE

OUTPUT:

OK, starting program...
--- 0.0020003318786621094 seconds ---
OK, program execution has ended.

Answer 4

with open('pagehead.section.htm')as f:contents=f.read()

Answer 5

I think the most natural way for achieving this is to define a function.

def read(filename):
    f = open(filename, 'r')
    output = f.read()
    f.close()
    return output

Then you can do the following:

output = read('pagehead.section.htm')

Answer 6

No need to import any special libraries to do this.

Use normal syntax and it will open the file for reading then close it.

with open("/etc/hostname","r") as f: print f.read() 

or

with open("/etc/hosts","r") as f: x = f.read().splitlines()

which gives you an array x containing the lines, and can be printed like so:

for line in x: print line

---

These one-liners are very helpful for maintenance - basically self-documenting.