Os.Path.Isdir • Os.Path.Join

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Meena Syamkumar Mike Doescher Relation to Recent Topics...

1 file objects are a type of iterator (lecture 24)

2 exceptions occur a lot with files (lecture 25) not found, out of space, no permissions, etc Learning Objectives Today

Basic file interactions • opening/closing • reading/writing

OS module • listdir, mkdir, exists, isdir, isfile, join

File exceptions

Encodings Learning Objectives Today

Basic file interactions • opening/closing • reading/writing

OS module • listdir, mkdir, exists, isdir, isfile, join

File exceptions

Encodings File objects

built-in open function

f = open(path)

file object file path # read data from f # OR # write data to f

f.close() File objects

built-in open function main.py: f = open(“file.txt”)

file object file path suppose we want to open file.txt # read data from f # OR # write data to f

f.close() File objects

built-in open function main.py: f = open( “data/movies.csv”)

file object file path

# read data from f # OR # write data to f

data/movies.csv

f.close() File objects

built-in open function main.py: f = open( “data/snapshots/A”)

file object file path

# read data from f # OR # write data to f

f.close()

data/snapshots/A File objects imagine a file object as a sandwich…

f = open(…) use file main.py: f = open(“file.txt”) f.close()

# read data from f # OR using file # write data to f Reasons for closing • avoid data loss • limited number of open files f.close() cleanup Learning Objectives Today

Basic file interactions • opening/closing • reading/writing

OS module • listdir, mkdir, exists, isdir, isfile, join

File exceptions

Encodings Reading a file

f = open(“file.txt”)

# read data from f # OR # write data to f I promise to always close my files f.close() Reading a file

f = open(“file.txt”)

data = f.read() Option 1

I promise print(data) to always close my files

data is: “I promise\nto always\nclose my files” f.close() read() method • fetch entire file contents • return as a string Reading a file

f = open(“file.txt”)

# read data from f Option 2 file objects are iterators! # OR # write data to f

f.close() yield keyword

The Vocabulary file object of Iteration contains a

dict.keys() generator function convert it dict.values() to a list returns a

list str tuple range generator object

is a is a is an

sequence iterator call next(f)

can be is an is an can give you an converted to a iterable

can go here

for x in : iterate over f with a for loop # some code yield keyword

The Vocabulary file object of Iteration contains a

dict.keys() generator function f = open("file.txt") convert it dict.values() lines = list(f) returns a to a list f.close() list str tuple range generator object f = open("file.txt") is a is a is an first = next(f) f.close() sequence iterator call next(f)

can be is an is an can give you an converted f = open("file.txt") to a iterable for l in f: print(l) can go here f.close() for x in : iterate over f with a for loop # some code Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

# read data from f # OR # write data to f I promise to always close my files f.close() Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

f.write(“hello”) f.write(“ world\n”) f.write(“!!!!!\n”) I promise to always close my files f.close()

let’s run it! Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

f.write(“hello”) f.write(“ world\n”) f.write(“!!!!!\n”)

f.close() opening with “w” is dangerous. It immediately wipes out your file.

(or creates a new one if there isn’t already a file.txt) Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

f.write(“hello”) f.write(“ world\n”) f.write(“!!!!!\n”) hello

f.close() Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

f.write(“hello”) f.write(“ world\n”) f.write(“!!!!!\n”) hello world

f.close() Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

f.write(“hello”) f.write(“ world\n”) f.write(“!!!!!\n”) hello world !!!!!! f.close() Write a file

“w” mode indicates we want to write to this file f = open(“file.txt”, “w”)

f.write(“hello”) f.write(“ world\n”) f.write(“!!!!!\n”) hello world !!!!!! f.close() be careful with newlines (write doesn't add them like print does) Learning Objectives Today

Basic file interactions • opening/closing • reading/writing

OS module • listdir, mkdir, exists, isdir, isfile, join

File exceptions

Encodings OS Module (Operating System)