Automation - Regex

credit link:https://www.datacamp.com/tutorial/python-regular-expression-tutorial

Regular Expression

short for Regex, are used to check if a pattern exists in a give string. classical regex use are internet search engines and file system finders.

• Regex in Python: import re and you can use it.
• Basic patterns: use re.match(pattern, sequence) to match two parameters.

wild card characters

• ```angular2html
  # ********group() method useage************
  statement = 'support@datacamp.com'
  match = re.search(r'([\w\.-]+)@([\w\.-]+)', statement)
  if statement:
  print("Email address:", match.group()) # return Email address: support@datacamp.com
  print("Username:", match.group(1)) # return Username: support
  print("Host:", match.group(2)) # return Host: datacamp.com
  

• . the period: match any char.
• ^ the caret: match the start of string
• $ match the end of the string.
• [abc]: match a or b or c.
• [a-zA-Z0-9] match any letter or number.
• \:
• -[x] escape character
• -[x] ordinary character
• -[x] in front of metachar to remove their special meaning
• \w: match any single letter, digit, underscore
• \W: match any character not part of\w.
• \s: match single whitespace: space, newline, tab, return
• \S: match any char not par of \s.
• \d: Lowercase d. Matches decimal digit 0-9.
• \D: Uppercase d. Matches any character that is not a decimal digit.
• \t: Lowercase t. Matches tab.
• \n : Lowercase n. Matches newline.
• \r : Lowercase r. Matches return.
• \A : Uppercase a. Matches only at the start of the string. Works across multiple lines as well.
• \Z: Uppercase z. Matches only at the end of the string.

Repetitions

• +: check if preceding char appears one or more time start frm that position.
• *: check if preceding char appears zero or more time start frm that position.
• ?: check if preceding char appears zero or one time start frm that position.
• {x}: Repeat exactly x number of times.
• {x,}: Repeat at least x times or more.
• {x, y}: Repeat at least x times but no more than y times.
• (): Creates a group when performing matches.
• <>: Creates a named group when performing matches.

search(), match() and findall()

• match() function checks for a match only at the beginning of the string (by default),
• search() function checks for a match anywhere in the string.
• findall() Finds all the possible matches in the entire sequence and returns them as a list of strings.
• sub(): sbustitute fucntion
• split(): split matched and return a list.

Compliation flag

• IGNORECASE (I) - Allows case-insensitive matches.
• DOTALL (S) - Allows . to match any character, including newline.
• MULTILINE (M) - Allows start of string (^) and end of string ($) anchor to match newlines as well.
• VERBOSE (X) - Allows you to write whitespace and comments within a regular expression to make it more readable.

shutil - High-level File Operations

• copyfile() copies the contents of the source to the destination and raises IOError if it does not have permission to write to the destination file.
• copy() function interprets the output name similar to the commandline cp
• copy2() similar to copy() but have more details including access and modifying time.
• copystat() copy meta data
• other shutil methods:

  copyfile()
  copyfileobj()
  copymode()
  copystat()
  copytree()
  copytree_verbose()
  disk_usage()
  get_archive_formats()
  get_unpack_formats()
  make_archive()
  move()
  rmtree()
  unpack_archive()
  which()
  which_regular_file()
  

  more useage details see this reference link: https://pymotw.com/3/shutil/

Things I want to know more:

• Regex implementation
• implementation of shutil to precess files from local file systems.