I want to create a text file and add data to it, line by line. If a data line already exists in the file, it should be ignored. Otherwise, it should be appended to the file.
You are almost certainly better to read the file and write a new changed version. In most circumstances it will be quicker, easier, less error-prone and more extensible.
If your file isn't that big, you could just do something like this:
added = set()
def add_line(line):
if line not in added:
f = open('myfile.txt', 'a')
f.write(line + '\n')
added.add(line)
f.close()
But this isn't a great idea if you have to worry about concurrency, large amounts of data being stored in the file, or basically anything other than something quick and one-off.
I did it like this,
def retrieveFileData():
"""Retrieve Location/Upstream data from files"""
lines = set()
for line in open(LOCATION_FILE):
lines.add(line.strip())
return lines
def add_line(line):
"""Add new entry to file"""
f = open(LOCATION_FILE, 'a')
lines = retrieveFileData()
print lines
if line not in lines:
f.write(line + '\n')
lines.add(line)
f.close()
else:
print "entry already exists"
if __name__ == "__main__":
while True:
line = raw_input("Enter line manually: ")
add_line(line)
if line == 'quit':
break
Related
As the title says, I made a file editing program with python.
Here is the code that I'm have a problem with:
#fileEditing.py
def fileError(file):
raise OSError("file {} does not exist".format(file))
class AccessFile():
def fileExists(self, file):
import os
return bool(os.path.exists(file))
def filecreate(self, file):
if not self.fileExists(file):
with open(file, "w") as f:
f.close()
else: raise OSError("file {} already exists".format(file))
def filedelete(self, file):
import os
if self.fileExists(file):
os.remove(file)
else: fileError(file)
def fileread(self, file):
#check if file exists
if self.fileExists(file):
#detect length of file
with open(file, "r") as f:
line = " "
x = 0
while line != "":
line = f.readline()
x += 1
#piece lines together in a list
filelines = []
with open(file, "r") as f:
for i in range(x - 1):
filelines.append(str(f.readline()))
#return a tuple
return tuple(filelines)
else: fileError(file)
def filewrite(self, file, line, text):
''' BUG: apparently this either overwrites the line its writing or appends
to the line its writing... make up your mind!'''
if self.fileExists(file):
#get file contents
filelines = list(self.fileread(file))
#see if line parameter is out of range or not
try:
filelines[line] = text
except IndexError:
for i in range(line - len(filelines)):
filelines.append("")
filelines.append(str(text) + "\n")
#apply changes
with open(file, "w") as f:
f.write("") #delete contents
with open(file, "w") as f:
for l in filelines:
f.write(l)
else: fileError(file)
def fileoverwrite(self, file, data):
#if there is no file to delete, it will make a new one
try:
self.filedelete(file)
except:
pass
self.filecreate(file)
x = 0
for line in data:
print(line)
self.filewrite(file, x, line)
x += 1
accessfile = AccessFile()
The bug is in the filewrite(self, file, line, text) function. When called, it either writes a new line (which is what I want it to do), appends to the line its supposed to replace, or just doesn't write any lines at all.
Say I want to write a python file with this program:
#pytesting.py
from fileEditing import *
file = "/Users/ashton/Desktop/Atom/Python/FileEditing/FileManager.py"
data = [
"from fileEditing import *",
"",
"class FileEditing():",
" def __init__(options, immutable_files):",
" self.options, self.immutable_files = options, immutable_files",
" ",
" def prompt():",
" ",
"",
"while True:",
" pass"
]
accessfile.fileoverwrite(file, data)
When I run it, it makes a file with accessfile.fileoverwrite(file, data), like its supposed to.
But thats where things get whacky.
(FileManager.py below)
from fileEditing import *
class FileEditing():
def __init__(options, immutable_files): self.options, self.immutable_files = options, immutable_files
def prompt():
while True:
If you know how to fix the filewrite(self, file, line, text), please let me know.
(I use python 2.7 but python 3 is fine)
So this is definitely a Python 3.x solution but you said that it is fine, don't know if it will work in Python 2.x but it is so simple it should:
def file_overwrite(self, file, data):
with open(file, 'w') as file:
file.write('\n'.join(data))
And you seemingly also need to fix that data list because it is missing a few commas. Also the fact that this is all in a class is a bit weird, you do nothing with the instance, they all might as well be separate functions or #classmethods or #staticmethods. Also several things could be improved with your other functions. For example you shouldn't open the file twice and count its lines to read it. Just do file.readlines() at it will return a list of all lines:
def fileread(self, file):
if self.fileExists(file):
with open(file) as file:
return file.readlines()
else:
fileError(file)
Then also import os once at the start of the file, you don't need to import it in every function where you use os, also:
with open(file, "w") as f:
f.close()
f.close() is completely pointless because the context manger closes the file anyways and also there is mode "x" which is specifically made for file creation and will raise an error if the file already exists: https://www.w3schools.com/python/python_file_handling.asp
I am trying to make a contact book application with command-line arguments. This is the code written so far to update the new contact details of a particular contact. args.name has the name of the contact. And args.number has the new number which needs to be updated.
How can I update the entire line? When I run this, it replaces the entire file, contacts.txt, with an empty string. This functionality will also help in the delete function.
thefile = open("contacts.txt","w+")
lines = thefile.readlines()
for line in lines:
if name in line:
line.replace(line,"Name: "+ args.name + " Number: "+args.number+ "\n")
You could firstly read the data from the file, create an empty string, append each line to the newly created string conditionally, and write(replace) the newly obtained string onto the existing file.
f1 = open('contacts.txt','r')
data = f1.readlines()
f1.close()
new_data = ""
for line in data:
if name in line:
update = line.replace(line,"Name: "+ args.name + " Number: "+args.number+ "\n")
new_data += update
else:
new_data += line
f2 = open('contacts.txt','w')
f2.write(new_data)
f2.close()
When you open a file with "w+" python erase the file !
First you whoud write two function: One that writes data and the other read data
def reader():
f = open("MYFILE.txt", "r")
lines = f.readlines()
f.close()
return lines
def writer(data):
f = open("MYFILE.txt", "w")
for i in data:
f.write(i)
f.close()
Then you can actualise lines how you want:
lines = reader()
for i in range(len(lines)):
if lines[i] == "Something\n":
lines[i] = "New_Value\n"
writer(lines)
I created a notepad text document called "connections.txt". I need to have some initial information inside it, several lines of just URLs. Each URL has it's own line. I put that in manually. Then in my program I have a function that checks if a URL is in the file:
def checkfile(string):
datafile = file(f)
for line in datafile:
if string in line:
return True
return False
where f is declared at the beginning of the program:
f = "D:\connections.txt"
Then I tried to write to the document like this:
file = open(f, "w")
if checkfile(user) == False:
usernames.append(user)
file.write("\n")
file.write(user)
file.close()
but it hasn't really been working correctly..I'm not sure what's wrong..am I doing it wrong?
I want the information in the notepad document to stay there ACROSS runs of the program. I want it to build up.
Thanks.
EDIT: I found something wrong... It needs to be file = f, not datafile = file(f)
But the problem is... It clears the text document every time I rerun the program.
f = "D:\connections.txt"
usernames = []
def checkfile(string):
file = f
for line in file:
if string in line:
return True
print "True"
return False
print "False"
file = open(f, "w")
user = "aasdf"
if checkfile(user) == False:
usernames.append(user)
file.write("\n")
file.write(user)
file.close()
I was working with the file command incorrectly...here is the code that works.
f = "D:\connections.txt"
usernames = []
def checkfile(string):
datafile = file(f)
for line in datafile:
if string in line:
print "True"
return True
print "False"
return False
user = "asdf"
if checkfile(user) == False:
usernames.append(user)
with open(f, "a") as myfile:
myfile.write("\n")
myfile.write(user)
The code that checks for a specific URL is ok!
If the problem is not erasing everything:
To write to the document without erasing everything you have to use the .seek() method:
file = open("D:\connections.txt", "w")
# The .seek() method sets the cursor to the wanted position
# seek(offset, [whence]) where:
# offset = 2 is relative to the end of file
# read more here: http://docs.python.org/2/library/stdtypes.html?highlight=seek#file.seek
file.seek(2)
file.write("*The URL you want to write*")
Implemented on your code will be something like:
def checkfile(URL):
# your own function as it is...
if checkfile(URL) == False:
file = open("D:\connections.txt", "w")
file.seek(2)
file.write(URL)
file.close()
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!
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
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)
I want to learn Python so I started writing my first program which is a phone book directory.
It has the options to add a name and phone number, remove numbers, and search for them.
Ive been stuck on the remove part for about 2 days now and just can't get it working correctly. I've been in the Python IRC and everything, but haven't been able to figure it out.
Basically, my program stores the numbers to a list in a file. I cannot figure out how to remove a particular line in the file but keep the rest of the file intact. Can someone please help me with this?
Some people have advised that it will be easier to do if I create a temp file, remove the line, then copy the remaining lines from the original file over to the temp file. Then write over the original file over with the temp file. So I have been trying this...
if ui == 'remove':
coname = raw_input('What company do you want to remove? ') # company name
f = open('codilist.txt', 'r') # original phone number listing
f1 = open('codilist.tmp', 'a') # open a tmp file
for line in f:
if line.strip() != coname.strip():
for line in f:
f1.write(line)
break # WILL LATER OVERWRITE THE codilist.txt WITH THE TMP FILE
else:
f1.write(line)
else:
print 'Error: That company is not listed.'
f1.close()
f.close()
continue
I assume your file contains something like <name><whitespace><number> on each line? If that's the case, you could use something like this for your if statement (error handling not included!):
name, num = line.strip().split()
if name != coname.strip():
# write to file
Suggestion:
Unless there is some specific reason for you to use a custom format, the file format json is quite good for this kind of task. Also note the use of the 'with' statement in these examples, which saves you having to explicitly close the file.
To write the information:
import json
# Somehow build a dict of {coname: num,...}
info = {'companyA': '0123456789', 'companyB': '0987654321'}
with open('codilist.txt', 'w') as f:
json.dump(info, f, indent=4) # Using indent for prettier files
To read/amend the file:
import json
with open('codilist.txt', 'r+') as f:
info = json.load(f)
# Remove coname
if coname in info:
info.pop(coname)
else:
print 'No record exists for ' + coname
# Add 'companyC'
info['companyC'] = '0112233445'
# Write back to file
json.dump(info, f, indent=4)
You'll need python2.6 or later for these examples. If you're on 2.5, you'll need these imports:
import simplejson as json
from __future__ import with_statement
Hope that helps!
Here is a pretty extensively rewritten version:
all the phone data is wrapped into a Phonebook class; data is kept in memory (instead of being saved and reloaded for every call)
it uses the csv module to load and save data
individual actions are turned into short functions or methods (instead of One Big Block of Code)
commands are abstracted into a function-dispatch dictionary (instead of a cascade of if/then tests)
This should be much easier to understand and maintain.
import csv
def show_help():
print('\n'.join([
"Commands:",
" help shows this screen",
" load [file] loads the phonebook (file name is optional)",
" save [file] saves the phonebook (file name is optional)",
" add {name} {number} adds an entry to the phonebook",
" remove {name} removes an entry from the phonebook",
" search {name} displays matching entries",
" list show all entries",
" quit exits the program"
]))
def getparam(val, prompt):
if val is None:
return raw_input(prompt).strip()
else:
return val
class Phonebook(object):
def __init__(self, fname):
self.fname = fname
self.data = []
self.load()
def load(self, fname=None):
if fname is None:
fname = self.fname
try:
with open(fname, 'rb') as inf:
self.data = list(csv.reader(inf))
print("Phonebook loaded")
except IOError:
print("Couldn't open '{}'".format(fname))
def save(self, fname=None):
if fname is None:
fname = self.fname
with open(fname, 'wb') as outf:
csv.writer(outf).writerows(self.data)
print("Phonebook saved")
def add(self, name=None, number=None):
name = getparam(name, 'Company name? ')
number = getparam(number, 'Company number? ')
self.data.append([name,number])
print("Company added")
def remove(self, name=None):
name = getparam(name, 'Company name? ')
before = len(self.data)
self.data = [d for d in self.data if d[0] != name]
after = len(self.data)
print("Deleted {} entries".format(before-after))
def search(self, name=None):
name = getparam(name, 'Company name? ')
found = 0
for c,n in self.data:
if c.startswith(name):
found += 1
print("{:<20} {:<15}".format(c,n))
print("Found {} entries".format(found))
def list(self):
for c,n in self.data:
print("{:<20} {:<15}".format(c,n))
print("Listed {} entries".format(len(self.data)))
def main():
pb = Phonebook('phonebook.csv')
commands = {
'help': show_help,
'load': pb.load,
'save': pb.save,
'add': pb.add,
'remove': pb.remove,
'search': pb.search,
'list': pb.list
}
goodbyes = set(['quit','bye','exit'])
while True:
# get user input
inp = raw_input("#> ").split()
# if something was typed in
if inp:
# first word entered is the command; anything after that is a parameter
cmd,args = inp[0],inp[1:]
if cmd in goodbyes:
# exit the program (can't be delegated to a function)
print 'Goodbye.'
break
elif cmd in commands:
# "I know how to do this..."
try:
# call the appropriate function, and pass any parameters
commands[cmd](*args)
except TypeError:
print("Wrong number of arguments (type 'help' for commands)")
else:
print("I didn't understand that (type 'help' for commands)")
if __name__=="__main__":
main()
Something simple like this will read all of f, and write out all the lines that don't match:
for line in f:
if line.strip() != coname.strip():
f1.write(line)
Ned's answer looks like it should work. If you haven't tried this already, you can set python's interactive debugger above the line in question. Then you can print out the values of line.strip() and coname.strip() to verify you are comparing apples to apples.
for line in f:
import pdb
pdb.set_trace()
if line.strip() != coname.strip():
f1.write(line)
Here's a list of pdb commands.
You probably don't want to open the temp file in append ('a') mode:
f1 = open('codilist.tmp', 'a') # open a tmp file
also, be aware that
for line in f:
...
f1.write(line)
will write everything to the file without newlines.
The basic structure you want is:
for line in myfile:
if not <line-matches-company>:
tmpfile.write(line + '\n') # or print >>tmpfile, line
you'll have to implement <line-matches-company> (there isn't enough information in the question to know what it should be -- perhaps if you showed a couple of lines from your data file..?)
I got this working...
if ui == 'remove':
coname = raw_input('What company do you want to remove? ') # company name
f = open('codilist.txt')
tmpfile = open('codilist.tmp', 'w')
for line in f:
if coname in line:
print coname + ' has been removed.'
else:
tmpfile.write(line)
f.close()
tmpfile.close()
os.rename('codilist.tmp', 'codilist.txt')
continue