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020 Files, Streams and related issues : Answers to exercises

Exercise 1

There is a file called environment.yml in the directory copy.

  • use Path to generate the a variable copy_dir containing the pathname of the copy directory
  • create a variable env_file which adds add the file environment.yml to this
  • check to see if the file exists
from pathlib import Path
# ANSWER

# There is a file called environment.yml in the directory copy.
# use Path to generate the a variable copy_dir containing the 
# pathname of the copy directory
copy_dir = Path('copy')

# create a variable env_file which adds add the file 
# environment.yml to this
env_file = copy_dir / 'environment.yml'
# or
env_file = Path(copy_dir,'environment.yml')

# check to see if the file exists
print(f'does {env_file} exist? {env_file.exists()}')

does copy/environment.yml exist? True

Exercise 2

Create a zero-sized file called hello.txt in a directory mystuff, using Path and show that it exists and is a file. Then delete the file and directory.

from pathlib import Path
# ANSWER
# import package

# Form the Path object for the file
myfile = Path('mystuff','hello.txt')

# Make sure the parent directory exists
myfile.parent.mkdir(parents=True,exist_ok=True)

# Create the zero-sized file
myfile.touch()

# Check it exists and is a file
print('=== now you see it ===')
print(f'Does {myfile.as_posix()} exist? {myfile.exists()}')
print(f'Is {myfile.as_posix()} a file? {myfile.is_file()}')

# delete the file 
myfile.exists() and myfile.is_file() and myfile.unlink()
# Check it exists and is a file
print("=== now you don't ===")
print(f'Does {myfile.as_posix()} exist? {myfile.exists()}')
print(f'Is {myfile.as_posix()} a file? {myfile.is_file()}')

# delete the directory -- the parent
mydir = myfile.parent
mydir.exists() and mydir.is_dir() and mydir.rmdir()
# Check it exists and is a dir
print("=== now you don't ===")
print(f'Does {mydir.as_posix()} exist? {mydir.exists()}')
print(f'Is {mydir.as_posix()} a file? {mydir.is_dir()}')

=== now you see it ===
Does mystuff/hello.txt exist? True
Is mystuff/hello.txt a file? True
=== now you don't ===
Does mystuff/hello.txt exist? False
Is mystuff/hello.txt a file? False
=== now you don't ===
Does mystuff exist? False
Is mystuff a file? False

Exercise 3

Create a zero-sized file in a new directory, and use Path.stat() to show it has size 0 bytes. Then tidy up by deleting the file and directory.

from pathlib import Path
# ANSWER
# import package
# very similar to exercise 2 but now we need to check the size

# Form the Path object for the file
myfile = Path('mystuff','hello.txt')

# Make sure the parent directory exists
myfile.parent.mkdir(parents=True,exist_ok=True)

# Create the zero-sized file
myfile.touch()

# print the file size
print(f'The file size of {myfile.as_posix()} is {myfile.stat().st_size} bytes')

# delete the file 
myfile.exists() and myfile.is_file() and myfile.unlink()
# delete the directory -- the parent
mydir = myfile.parent
mydir.exists() and mydir.is_dir() and mydir.rmdir()

The file size of mystuff/hello.txt is 0 bytes

Exercise 4

Use Path.touch() to update the modification time for the file bin/README and demonstrate that you have done this and that is the same as the current time (now).

from pathlib import Path
from datetime import datetime
# ANSWER
# import packages

readme = Path('bin','README')

modified = readme.stat().st_mtime
h_modified = datetime.fromtimestamp(modified)

print(f'Before touch: time of most recent modification for {readme} is {h_modified}')

# touch the file
readme.touch()
modified = readme.stat().st_mtime
h_modified = datetime.fromtimestamp(modified)

print(f'After touch: time of most recent modification for {readme} is {h_modified}')
print(f'Now it is {datetime.now()}')

Before touch: time of most recent modification for bin/README is 2022-09-29 15:46:20.737117
After touch: time of most recent modification for bin/README is 2022-10-21 16:19:25.448961
Now it is 2022-10-21 16:19:25.452844

Exercise 5

  • Use Path to show the file permissions of all files that end .md in the directory . (current directory)
from pathlib import Path
# ANSWER
# import packages

# Use Path to show the file 
# permissions of all files that end .md 
# in the directory . (current directory)

# Path().cwd() gives the current directory (.)
here = Path().cwd()

# clearly, this needs glob the pattern will be *.md
# use * to put output as list of arguments
print(*here.glob('*.md'))

/nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/Install.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/InstallGDAL.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/OutsideInstall-Docker-owner.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/OutsideInstall-Docker.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/OutsideInstall-Local.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/OutsideInstall-Requirements.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/README.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/TIMETABLE.md /nfs/cfs/home3/Ucour1/coursd0/geog0111/notebooks/Using-the-course-notes.md

Exercise 6

Copy the file geog0111/cylog.py to a new directory myfile and confirm the size of the file copied. Tidy up by deleting the copied file.

from pathlib import Path
# ANSWER
# import packages

# Copy the file geog0111/cylog.py to a new directory 
# myfile and confirm the size of the file copied. 
# Tidy up by deleting the copied file.

# setup Path object for ifile 
ifile = Path('geog0111','cylog.py')

# setup Path object for ofile 
ofile = Path('myfile',ifile.name)
# create directory 
ofile.parent.mkdir(parents=True,exist_ok=True)

# read ifile, write to ofile (text)
nbytes = ofile.write_text(ifile.read_text()) #for binary files
print(f'{nbytes} bytes written for {ofile}')

# tidy up and remove the file
ofile.unlink()
ofile.parent.rmdir()

9249 bytes written for myfile/cylog.py

Exercise 8

  • write code to read from the json-format file bin/copy/environment.json into a dictionary called json_data.
  • print out the dictionary keys.
  • print the file size of the json-format file in KB to two decimal places.
# ANSWER
# write code to read from the json-format file 
# bin/copy/environment.json 
# into a dictionary called json_data.
json_file = Path('bin/copy/environment.json')

# use with ... as ... as we have been shown
with json_file.open('r') as f:
    json_data = json.load(f)

# print out the dictionary keys.
print(json_data.keys())

# print the file size of the 
# json-format file in KB to two decimal places.
print(f'file {json_file} size {json_file.stat().st_size / 1024 : .2f} KB')

dict_keys(['name', 'channels', 'dependencies'])
file bin/copy/environment.json size  0.78 KB

Exercise 9

  • check that the file images/ucl.png exists and print modification time and the file size in KB to two decimal places
  • make a directory myfiles and copy the file images/ucl.png to this directory
  • show the file size of myfiles/ucl.png, the modification time, and the time now
  • after that, tidy up by deleting the file myfiles/ucl.png and the directory myfiles. Confirm that you have done this.

You will need to know how many Bytes in a Kilobyte, and how to format a string to two decimal places. You will also need to remember how to use if statements.

from pathlib import Path
from datetime import datetime
# ANSWER
# import packages

# check that the file images/ucl.png exists and 
# print modification time and the file size in KB to two decimal places

# make a directory myfiles and copy the file images/ucl.png 
# to this directory
# show the file size of myfiles/ucl.png, the 
# modification time, and the time now
# after that, tidy up by deleting the file 
# myfiles/ucl.png and the directory myfiles. 
# Confirm that you have done this.

# check that the file images/ucl.png exists and 
# print modification time and the file size in KB to two decimal places

ifile = Path('images','ucl.png')
# check that the file images/ucl.png exists and 
print(f'The file {ifile} exists?: {ifile.exists()}')
# print the file in KB to two decimal places
# 1 KB = 1024 bytes
ifile_bytes = ifile.stat().st_size
print(f'The file {ifile} size: {ifile_bytes} B')
# in KB using .2f format for 2 dp
ifile_size_kb = ifile.stat().st_size / 1024
print(f'The file {ifile} size: {ifile_size_kb : .2f} KB')

# show the file size of myfiles/ucl.png, the 
# modification time, and the time now

modified = ifile.stat().st_mtime
h_modified = datetime.fromtimestamp(modified)
print(f'The file {ifile} modification time: {h_modified}')

print("\nconfirm with ls -lh")
!ls -lh {ifile}

# make a directory myfiles and copy the file images/ucl.png to this directory
ofile = Path('myfiles',ifile.name)
# mkdir the parent
ofile.parent.mkdir(parents=True,exist_ok=True)
# copy text file with read_text() and write_text()
ofile.write_bytes(ifile.read_bytes()) #for binary files

print('\n==== After copying')
# confirm size
print(f'The file {ofile} size: {ofile.stat().st_size / 1024 : .2f} KB')

# mod time
modified = ofile.stat().st_mtime
h_modified = datetime.fromtimestamp(modified)
print(f'The file {ofile} modification time: {h_modified}')
# now time
print(f'Time now is {datetime.now()}')

# tidy up
ofile.unlink()
ofile.parent.rmdir()

The file images/ucl.png exists?: True
The file images/ucl.png size: 1956 B
The file images/ucl.png size:  1.91 KB
The file images/ucl.png modification time: 2022-09-29 15:46:26.616106

confirm with ls -lh
-rw-r--r-- 1 coursd0 ucaac2 2.0K Sep 29 15:46 images/ucl.png

==== After copying
The file myfiles/ucl.png size:  1.91 KB
The file myfiles/ucl.png modification time: 2022-10-21 16:19:26.415919
Time now is 2022-10-21 16:19:26.425067
Last update: September 29, 2021