Write a Python program called gashlycrumb.py that takes a letter of the alphabet as an argument and looks up the line in a -f|--file argument (default gashlycrumb.txt) and prints the line starting with that letter. It should generate usage with no arguments or for -h|--help:

$ ./gashlycrumb.py
usage: gashlycrumb.py [-h] [-f str] str
gashlycrumb.py: error: the following arguments are required: str
$ ./gashlycrumb.py -h
usage: gashlycrumb.py [-h] [-f str] str

Gashlycrumb

positional arguments:
  str                 Letter

optional arguments:
  -h, --help          show this help message and exit
  -f str, --file str  Input file (default: gashlycrumb.txt)

You can see the structure of the default "gashlycrumb.txt" file:

$ head -3 gashlycrumb.txt
A is for Amy who fell down the stairs.
B is for Basil assaulted by bears.
C is for Clara who wasted away.

You will use the first character of the line as a lookup value:

$ ./gashlycrumb.py a
A is for Amy who fell down the stairs.
$ ./gashlycrumb.py z
Z is for Zillah who drank too much gin.

If given a value that does not exist in the list of first characters on the lines from the input file (when searched with regard to case), you should print a message:

$ ./gashlycrumb.py 3
I do not know "3".
$ ./gashlycrumb.py CH
I do not know "CH".

If provided a --file argument that does not exist, your program should exit with an error and message:

$ ./gashlycrumb.py -f sdfl b
usage: gashlycrumb.py [-h] [-f str] str
gashlycrumb.py: error: argument -f/--file: can't open 'sdfl': \
[Errno 2] No such file or directory: 'sdfl'

Hints:

• To validate that the --filename is actually a readable file, look into using argparse.FileType('r') to describe the type of the --file argument so that argparse will do the check and create the error.
• A dictionary is a natural data structure that you can use to associate some value like the letter "A" to some phrase like "A is for Amy who fell down the stairs."
• Once you have an open file handle to the --filename (which is exactly what you get when use argparse.FileType), you can read the file line-by-line with a for loop.
• Each line of text is a string. How can you get the first character of a string?
• Using that first character, how can you set the value of a dict to be the key and the line itself to be the value?
• Once you have constructed the dictionary of letters to lines, how can you check that the user's letter argument is in the dictionary?
• Can you solve this without a dict?