How to Pass a .Txt File to a Function in Python

How can I pass a .txt file as a function parameter

I think you want

def my_function(filepath):
    data = open(filepath, "r")
    ...

and then

my_function("/filepath/some_file_name.txt")

or better:

def my_function(data):
    ...

and then

with open("/filepath/some_file_name.txt", "rb") as data:
    my_function(data)

The latter version lets you pass in any file-like object to my_function().

Update: if you want to get fancy and allow file names or file handles:

def my_func(data):
    if isinstance(data, basestring):
        with open(data, 'rb') as f:
            return my_func(f)
    ...

How to pass a .txt file to a function in Python?

Let's convert this task in many little and easier to solve tasks.

First function

def string_to_tuple(person_string):
    """ Converts a string into a tuple.
    person_string must be in the following format: "first_name last_name salary"
    A tuple of the following format is returned: (first_name, last_name, salary)
    salary must be an int. If it can be a float change int to float

    e.g.
    >>> string_to_tuple("John Miller 100")
    ('John', 'Miller', 100)
    """
    first_name, last_name, salary = person_string.split(" ")
    return first_name, last_name, int(salary)

This function takes a string splits it at whitespace and returns a tuple. Note that no error checking was done. You should, later on, check if the input is valid.

Second function

def tuple_to_string(person_tuple):
    """Converts a tuple with person data into a string. This is is inverse function to `string_to_tuple`.

    person_tuple must be in the following format: (first_name, last_name, salary)
    A string of the following format is returned: "first_name last_name salary"

    e.g.
    >>> string_person = "John Miller 100"
    >>> string_person_2 = tuple_to_string(string_to_tuple(string_person))
    >>> string_person == string_person_2
    True
    >>> tuple_to_string(('John', 'Miller', 100))
    'John Miller 100'
    """
    string_person = " ".join(str(i) for i in person_tuple)
    return string_person

Here you join a tuple back into a string. Before you can join you need to convert every item into a string (str(i)).

Reading from a file

For reading, you should use the with. This ensures, that the file is always closed when it is not used anymore.

Opening a file:

path_to_file = "my_file.txt"
with open(path_to_file, "r") as file:
    content = file.read() # alternatives: file.readlines() or file.readline()

print(content) # To ensure the content was correctly read. Not needed in the later application

The path of the file must be either relative to your current working directory (Where your script is) or absolute.

Difference between file and path

There is a difference between a path of a file (path_to_file) and an actually opened file (file). The path can be entered by the user and you have to use it to open the file. The user cannot enter a file object.

>>> type(path_to_file)
<class 'str'>
>>> type(file)
<class '_io.TextIOWrapper'>

A possible comparison that is easier to understand may be the following: Think of a public library: The library has books and every book has a title. If you want to read a book, you need to find this book by title, get an exemplar open it and read it. In this example, a book title is a filename and a book is a file.

Read from file and call function

Now the last step is to put all things together. So first read from the file and then call the previously created functions. The read depends on your file structure. I just assume you have in each line data for a new person.

with open(path_to_file, "r") as file:
    for line in file.readlines():
        tuple_person = string_to_tuple(line)
        print(tuple_person) # verify output

If you have any questions to a part your welcome to ask it in the comments.

Edit

Adjustments based on file content

One line in the file is as follows: Chelsea Right-back Davide Zappacosta 20,000,000

You need to expand the tuples:

original: first_name, last_name, salary

new: team, position, first_name, last_name, salary

Note: For now just keep the salary as s string and not convert it to an int or float.

original: return first_name, last_name, int(salary)

new: return team, position, first_name, last_name, salary

and

original: string_person = " ".join(str(i) for i in person_tuple)

new: string_person = " ".join(person_tuple)

Resources

reading-and-writing-files
split method
join method
too-many-values-to-unpack Should be a hint how to solve your error. If this doesn't help, post the content of the file you want to read in.

how to pass a filename as function parameter in python?

As others has already answered, the problem you're having with your code is that you're not opening the file you're giving the function. You're trying to open a string-representation of the variable, not the actual variable.

Here is the solution you're after:

def string_in_file(fname, s):
    # Use a context-manager to automatically
    # handle closing of files after you're done.
    with open(fname, "r") as F:
        # Read one line at a time, keeping only
        # that one line in memory.
        for line in F.readlines():
            if s in line:
                return True
        # If none of the lines in the for-loop
        # are True, then the string is not in the file.
        return False

Or if you want a single-line solution (which doesn't work the same way, but gives similar results):

string_in_file = lambda fname, s: any(s in line for line in open(fname))

Python Function: using a batch file to pass parameters from .txt file to python function and execute function

If you have a file called parameters.txt with data

foo
bar
foobar

And a function

def my_function(some_text):
    print("I was called with " + some_text)

Then you can do this to pass every line of the file to the function:

with open('parameters.txt', 'r') as my_file:
    for line in my_file:
        # remove the # and space from the next line to enable output to console:
        # print(line.rstrip())

        my_function(line.rstrip())

Note that the rstrip() method in all my examples strips off the trailing newline (as well as other trailing whitespace) that would otherwise be part of each line.

If your parameter file has a header, as in your example, you have multiple possibilities to skip that.

For example you can read all lines at once into a list and then iterate over a subset:

with open('parameters.txt', 'r') as my_file:
    all_lines = [line.rstrip() for line in my_file.readlines()]

# print(all_lines)

for line in all_lines[1:]:
    # print(line)

    my_function(line)

However, that would just ignore the header. If you accidentally passed a wrong file or one that has invalid content, this could spell trouble.

It's better to check whether the header of the file is correct. You can just expand the code from above:

with open('parameters.txt', 'r') as my_file:
    all_lines = [line.rstrip() for line in my_file.readlines()]

# print(all_lines)

if all_lines[0] != 'COM_PORTS':
    raise RuntimeError("file has wrong header")

for line in all_lines[1:]:
    # print(line)

    my_function(line)

Or you can do this inside the loop, for instance:

expect_header = True

with open('parameters.txt', 'r') as my_file:
    for line in my_file:
        stripped = line.rstrip()
        if expect_header:
            if stripped != 'COM_PORTS':
                raise RuntimeError("header of file is wrong")

            expect_header = False
            continue

        # print(stripped)

        my_function(stripped)

Or you can use an generator expression to check the header outside of the loop:

with open('parameters.txt', 'r') as my_file:
    all_lines = (line.rstrip() for line in my_file.readlines())

if next(all_lines) != 'COM_PORTS':
    raise RuntimeError("file has wrong header")

for line in all_lines:
    # print(line)

    my_function(line)

I would likely prefer this last one, as it is has a clear structure and no magic numbers (such as 0 and 1, referring to which line is the header and how many to skip, respectively) and it doesn't need to read all lines into memory at once.

However, the solution further above that reads all lines into a list at once is probably better if you want to do further processing on them as the data is already available in that case and you don't need to read the file again.

passing files and values as parameter to a function in python

I would create a little class (give it a useful name) to encapsulate your data.
If your files grow you only have to change your create_lats

min_length = 1
max_length = 30

# delays
delay = 100

# Speed of light
c_vaccum = 3e8

#Little class to keep our data in one place 
class Lat:
    def __init__(self, filename, factor):
        self.filename = filename
        self.factor = factor
        self.file = open(filename, "w") #let the class open the file


#now our function needs only one parameter, neat!
def latcalc(lat):
    target_name = 0

    for length in range(min_length, max_length):
        if length < 2:
            target_name += (length / (lat.factor * c_vaccum)) #acces the class variable
        elif length == 2:
            target_name += delay
        else:
            target_name = target_name

        myline = "%s\t%s\n" % (length, target_name)
        lat.file.write(myline)


def create_lats():
    lats = []
    lats.append(Lat("file1.txt", 0.4))
    lats.append(Lat("file2.txt", 0.8))
    lats.append(Lat("file3.txt", 1))
    return lats


#loop over your lats created in create_lats
for lat in create_lats():
    latcalc(lat)
    lat.file.close() #close the file

Python - import list from txt file, iterate, and pass as argument

readlines returns a list, and you want to perform split on a string, so you need to use read instead to return a string.

A possible solution would be:

def iterateList():
    with open('lib.txt') as f:
        data = f.read().split(',')
    while True:
        for i in data:
            otherFunction(i)

How to write a function that takes in the name of a file as the argument in Python?

Your function should take a string filename as a parameter, like this:

def return_exactly_one(filename):
    test = open(filename, "r")
    ...

and then you would call the function like:

return_exactly_one("test.txt")