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)
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!
list. Moving the open outside the function may make it more flexible (it can now be passed arbitrary file-like objects opened in different ways), but if the function is supposed to open the file the same way, it just means all callers are doing the same work, when they could just pass the file name and keep the common file open code in the function.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.)
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
splitlines to remove newlines from lines and/or blank line elimination, you're better off either slurping as a single value and splitting, or processing line by line. Reading all the lines to a list, joining the list, then spliting it up again is wasted work/memory (you're storing three copies of file data at once).contents = f.read().splitlines() (which drops peak memory one copy of file data as a block and two copies of list of lines to one of each), or without blank lines (and still only two copies in memory at once), contents = list(filter(None, f.read().splitlines())). To only have one copy as a list, no complete copies of the data in memory, process it line by line and both strip and filter as you go: contents = [x for x in (x.rstrip('\r\n') for x in f) if x]contents = list(filter(None, map(str.rstrip, f))) which moves all the work to the C layer in CPython, at the expense of using map and filter, generally considered less Pythonic. Stripping only newlines is also possible this way, it's just uglier: from operator import methodcaller, contents = list(filter(None, map(methodcaller('strip', '\r\n'), f)))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.
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)
close instead of implicit close via with as your primary example is just encouraging bad practices.
readlinesmethod on files is redundant with files iterator behavior; in Python 3,f.readlines()is more verbose and no faster than (and in fact, in my tests, fractionally slower than)list(f), and makes people write bad code by obscuring the iterator nature of files. In reality, you rarely want to do eitherf.readlines()orlist(f), because you usually want to iterate the file directly, either to process lines one at a time and discard them, or if you need alist, you still want some preprocessing (e.g. stripping newlines and/or blank lines) that as you iterate.