cpsc 236 files

open function

open(file, mode)

close function

close()

read method

file object method that reads entire file contents into memory, only works if file has been opened for reading, contents returned as a string

read position

marks the location of the next item to be read from a file

reading data from a file

f = open(“demofile.txt“, “r“)

print(f.read())

returns the 5 first characters of the file

f = open(“demofile.txt“, “r“)

print(f.read(5))

seek

f=open(“test.txt“, “r“)

f.seek(3)

f.read()

starts reading from the 3rd character

readline method

file object method that reads a line from the file, line returned as a string including ‘\n’

read one line of the file

f = open(“demofile.txt“, “r“)

print(f.readline())

read two lines of the file

f = open(“demofile.txt“, “r“)

print(f.readline())

print(f.readline())

readlines() method

returns a list of strings, where the first element is the contents of the first line, the second element is the contents of the second line, and so on

readlines syntax

f = open(“demofile.txt“, “r“)

print(f.readlines())

open a file in write mode and close manually

outfile = open(“text.txt“, “w“)

outfile.write(“Test“)

outfile.close()

str function

converts value to string

for loop with file syntax

for line in file_object:

statements

opens a text file in write mode and automatically closes it

with open(“text.txt“, “w“) as outfile:

outfile.write(“Test“)

code that opens a text file in read mode and automatically closes it

with open(“test.txt“, “r“) as infile:

print(infile.readline())

write method of a file object

write(str)

write one line to a text file

with open(“members.txt“, “w“) as file:

file.write(“John Cleese \n“)

append one line to a text file

with open(“members.txt“, “a“) as file:

file.write(“Eric Idle \n“)

use a loop to read each line of the file

with open(“members.txt“) as file:

for line in file:

print(line, end=””)

print()

read the entire file as a string

with open(“members.txt“) as file:

contents = file.read()

print(contents)

read entire file as a list

with open(“members.txt“) as file:

members = file.readlines()

print(members[0], end=””)

print(members[1])

read each line of the file

with open(“members.txt“) as file:

member1=file.readline()

print(member1, end=””)

member2=file.readline()

print(member2)

write the items in a list to a file

members = [“John Cleese“, “Eric Idle“]

with open(“members.txt“, “w“) as file:

for m in members:

file.write(m, “\n“)

read line in a file into a list

members = []

with open(“members.txt“) as file:

for line in file:

line = line.replace(“\n“, ““)

members.append(line)

print(members)

write the items in a list to a file

years = [1975, 1979, 1983]

with open(“years.txt“, “w“) as years_file:

for year in years:

years_file.write(str(year) + “\n“)

read items in a list from a file

years = []

with open(“years.txt”) as file:

for line in file:

line = line.replace(“\n“, ““)

years.append(int(line))

print(years)

writer function for csv

writer(file)

writerows method for csv

writerows(rows)

write the list to a csv file

with open(“movies.csv“, “w“, newline=””) as file:

writer = csv.writer(file)

writer.writerows(movies)

reader function for csv

reader(file)

read data from csv file

with open(“movies.csv“, newline=””) as file:

reader = csv.reader(file)

for row in reader:

print(row[0] + “ (“ + str(row[1]) + “)“)

pickle module

binary protocols for serializing and de-serializing a python object, two main methods of dump and load

dump method

dumps an object to a file object, dump(object, bfile)

load method

loads an object from a file object, load(bfile)

write an object to a binary file

with open(“movies.bin“, “wb“) as file:

pickle.dump(movies, file)

read an object from a binary file

with open(“movies.bin“, “rb“) as file:

movie_list = pickle.load(file)

print(movie_list)

os module

provides an interface to operating system function calls

os module syntax

import os

myfile=open(“myfile.txt“, “r“)

file_info = os.stat(“mfile.txt“)

os.remove(“myfile.txt“)

os.walk()

“walks“ a directory tree, visiting each subdirectory in the specified path