add lab2 in English
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Jakub Pokrywka
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laboratoria2/info_en.md
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laboratoria2/info_en.md
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# DJFZ 2020 laboratories 2
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## Upgrade repo
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First, please update your repo. There are new tasks.
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`git pull git@git.wmi.amu.edu.pl:filipg/djfz-2020.git`
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## Tasks to do on your own
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Tasks from section B and C - regular expressions. Deadline is till the end of November 22nd.
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Please do all B tasks. These are the same tasks as A, but differ in the solution method. This time please use regular expressions.
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When writing the solutions, please pay attention to the diffrence in complexity and execution time between regular expressions (B) and solutions based on basic mechanisms (A).
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Each of you is assigned exactly 4 C tasks (in total these tasks will constitute an "easy task" with
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section C, although you don't have to do them all).
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Note: which task falls to you depends on the student index number! The tasks are grouped into 4 blocks:
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- TaskC00-TaskC09 - the remainder from dividing by 10,
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- TaskC10-TaskC36 - the remainder from dividing by 27,
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- TaskC37-TaskC43 - the remainder from dividing by 7,
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- TaskC44-TaskC48 - the remainder from dividing by 5.
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Please check in the repository which task from each block is assigned to you. So each of you has exactly one task from each of these 4 blocks.
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You can get a total of 16 points for the second laboratory.
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## Regular expressions
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We will do regular expressions based on python3. Documentation: https://docs.python.org/3/library/re.html.
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### Basic functions
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search - returns the first match in the substring
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findall - returns a list of all matches (not overlapping)
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match - returns the match from the beginning of the string
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These are just the basic functions that we will use. The documentation describes them all.
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### match object
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```
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import re
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answer = re.search('na','banana')
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print(answer)
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print(answer.start())
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print(answer.end())
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print(answer.group())
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answer = re.search('na','kabanos')
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print(answer)
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type(answer)
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if answer:
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print(answer.group())
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else:
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pass
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```
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### Metacharacters
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- [] - set of characters
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- . - any sign
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- ^ - beginning of a string
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- $ - end of the a string
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- ? - the character preceding is or is not present
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- \* - zero or more appearances of the character preceding
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- \+ - one or more appearances of the character preceding
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- {} - exactly as many appearances of the character preceding
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- | - or
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- () - group
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- \ - escape character
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- \d a digit
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- \D every character, but digit
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- \s a whitespace
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- \S every character, but whitespace
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### Flags
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You can use special flags, such as in example:
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`re.search('ma', 'AlA Ma KoTa', re.IGNORECASE)`.
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### Examples (lab explanations)
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To study, it is better to use interactive python interpreter, preferably ipython.
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```
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import re
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text = 'Ala has a cat and hammock, and 150 bananas.
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re.search('ma',text)
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re.match('ma',text)
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re.match('Ala ma',text)
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re.findall('ma',text)
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re.findall('[mn]a',text)
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re.findall('[0-9]',text)
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re.findall('[0-9abc]',text)
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re.findall('[a-z][a-z]ma[a-z]',text)
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re.findall('[a-zA-Z][a-zA-Z]ma[a-zA-z0-9]',text)
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re.findall('\d',text)
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re.search('[0-9][0-9][0-9]',text)
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re.search('[\d][\d][\d]',text)
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re.search('\d{2}',text)
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re.search('\d{3}',text)
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re.search('\d+',text)
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re.search('\d+ bananas',text)
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re.search('\d* bananas', 'Ala has a lot of bananas')
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re.search('\d* bananas',text)
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re.search('ma \d? bananas','Ala has 5 bananas')
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re.search('ma ?d? bananas','Ala has bananas')
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re.search('ma(\d)? bananas', 'Ala has bananas')
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re.search('\d+ bananas', 'Ala has 10 bananas or 20 bananas')
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re.search('\d+ bananas$', 'Ala has 10 bananas or 20 bananas')
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text = 'Ala has a cat and hammock, and 150 bananas.
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re.search('\d+ bananas',text)
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re.search('\d+\sbananów',text)
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re.search('kota . hamak',text)
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re.search('cat . hammock','Ala has a cat with a hammock')
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re.search('cat .* hammock','Ala has a cat or hammock')
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re.search('\.',text)
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re.search('cat|psa','Ala has a cat or hammock')
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re.findall('cat|psa','Ala has a cat or a dog')
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re.search('cat (i|or) dog','Ala has a cat or dog')
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re.search('mam (cat).*(cat|psa)','I have a cat. Ala has a dog.').group(0)
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re.search('mam (cat).*(cat|psa)','I have a cat. Ala has a dog.').group(1)
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re.search('mam (cat).*(cat|psa)','I have a cat. Ala has a dog.').group(2)
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```
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