# Reference guide: Python concepts from module 4
## File operations
The following functions, methods, and keywords are used with operations involving files.
### with
Handles errors and manages external resources
#### with open("logs.txt", "r") as file:
Used to handle errors and manage external resources while opening a file; the variable file stores the file information while inside of the with statement; manages resources by closing the file after exiting the with statement
### open()
Opens a file in Python
with open("login\_attempts.txt", "r") as file:
Opens the file "login\_attempts.txt" in order to read it ("r")
with open("update\_log.txt", "w") as file:
Opens the file "update\_log.txt" into the variable file in order to write over its contents ("w")
with open(import\_file, "a") as file:
Opens the file assigned to the import\_file variable into the variable file in order to append information to the end of it ("a")
### as
Assigns a variable that references another object
with open("logs.txt", "r") as file:
Assigns the file variable to reference the output of the open() function
### .read()
Converts files into strings; returns the content of an open file as a string by default
with open("login\_attempts.txt", "r") as file:
file\_text = file.read()
Converts the file object referenced in the file variable into a string and then stores this string in the file\_text variable
### .write()
Writes string data to a specified file
with open("access\_log.txt", "a") as file:
file.write("jrafael")
Writes the string "jrafael" to the "access\_log.txt" file; because the second argument in the call to the open() function is "a", this string is appended to the end of the file
## Parsing
The following methods are useful when parsing data.
### .split()
Converts a string into a list; separates the string based on the character that is passed in as an argument; if an argument is not passed in, it will separate the string each time it encounters whitespace characters such as a space or return
approved\_users = "elarson,bmoreno,tshah".split(",")
Converts the string "elarson,bmoreno,tshah" into the list \["elarson","bmoreno","tshah"\] by splitting the string into a separate list element at each occurrence of the "," character
removed\_users = "wjaffrey jsoto abernard".split()
Converts the string "wjaffrey jsoto abernard" into the list \["wjaffrey","jsoto","abernard"\] by splitting the string into a separate list element at each space
### .join()
Concatenates the elements of an iterable into a string; takes the iterable to be concatenated as an argument; is appended to a character that will separate each element once they are joined into a string
approved\_users = ",".join(\["elarson", "bmoreno", "tshah"\])
Concatenates the elements of the list \["elarson","bmoreno","tshah"\] into the string "elarson,bmoreno,tshah" , separating each element with the "," character within the string