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