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Asabeneh committed Jul 8, 2021
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Expand Up @@ -21,7 +21,7 @@
- [📘 Day 18](#-day-18)
- [Regular Expressions](#regular-expressions)
- [The *re* Module](#the-re-module)
- [Functions in *re* Module](#functions-in-re-module)
- [Methods in *re* Module](#methods-in-re-module)
- [Match](#match)
- [Search](#search)
- [Searching for All Matches Using *findall*](#searching-for-all-matches-using-findall)
Expand All @@ -37,6 +37,9 @@
- [Quantifier in RegEx](#quantifier-in-regex)
- [Cart ^](#cart-)
- [💻 Exercises: Day 18](#-exercises-day-18)
- [Exercises: Level 1](#exercises-level-1)
- [Exercises: Level 2](#exercises-level-2)
- [Exercises: Level 3](#exercises-level-3)

# 📘 Day 18

Expand All @@ -52,11 +55,11 @@ After importing the module we can use it to detect or find patterns.
import re
```

### Functions in *re* Module
### Methods in *re* Module

To find a pattern we use different set of *re* character sets that allows to search for a match in a string.

* *re.match()*: searches only in the beginning of the first line of the string and returns matched objects if found, else returns none.
* *re.match()*: searches only in the beginning of the first line of the string and returns matched objects if found, else returns None.
* *re.search*: Returns a match object if there is one anywhere in the string, including multiline strings.
* *re.findall*: Returns a list containing all matches
* *re.split*: Takes a string, splits it at the match points, returns a list
Expand Down Expand Up @@ -89,6 +92,16 @@ print(substring) # I love to teach

As you can see from the example above, the pattern we are looking for (or the substring we are looking for) is *I love to teach*. The match function returns an object **only** if the text starts with the pattern.

```py
import re

txt = 'I love to teach python and javaScript'
match = re.match('I like to teach', txt, re.I)
print(match) # None
```

The string does not string with *I like to teach*, therefore there was no match and the match method returned None.

#### Search

```py
Expand Down Expand Up @@ -129,10 +142,9 @@ I recommend python for a first programming language'''
# It return a list
matches = re.findall('language', txt, re.I)
print(matches) # ['language', 'language']

```

As you can see, the word language was found two times in the string. Let's practice some more.
As you can see, the word *language* was found two times in the string. Let us practice some more.
Now we will look for both Python and python words in the string:

```py
Expand All @@ -145,7 +157,7 @@ print(matches) # ['Python', 'python']

```

Since we are using *re.I* both lowercase and uppercase letters are included. If we don't have that flag, then we will have to write our pattern differently. Let's check it out:
Since we are using *re.I* both lowercase and uppercase letters are included. If we do not have the re.I flag, then we will have to write our pattern differently. Let us check it out:

```py
txt = '''Python is the most beautiful language that a human being has ever created.
Expand Down Expand Up @@ -173,24 +185,23 @@ match_replaced = re.sub('[Pp]ython', 'JavaScript', txt, re.I)
print(match_replaced) # JavaScript is the most beautiful language that a human being has ever created.
```

Let's add one more example. The following string is really hard to read unless we remove the % symbol. Replacing the % with an empty string will clean the text.
Let us add one more example. The following string is really hard to read unless we remove the % symbol. Replacing the % with an empty string will clean the text.

```py

txt = '''%I a%m te%%a%%che%r% a%n%d %% I l%o%ve te%ach%ing.
txt = '''%I a%m te%%a%%che%r% a%n%d %% I l%o%ve te%ach%ing.
T%he%re i%s n%o%th%ing as r%ewarding a%s e%duc%at%i%ng a%n%d e%m%p%ow%er%ing p%e%o%ple.
I fo%und te%a%ching m%ore i%n%t%er%%es%ting t%h%an any other %jobs.
I fo%und te%a%ching m%ore i%n%t%er%%es%ting t%h%an any other %jobs.
D%o%es thi%s m%ot%iv%a%te %y%o%u to b%e a t%e%a%cher?'''

matches = re.sub('%', '', txt)
print(matches)
```

```sh
I am teacher and I love teaching.
There is nothing as rewarding as educating and empowering people.
I found teaching more interesting than any other jobs.
Does this motivate you to be a teacher?
I am teacher and I love teaching.
There is nothing as rewarding as educating and empowering people.
I found teaching more interesting than any other jobs. Does this motivate you to be a teacher?
```

## Splitting Text Using RegEx Split
Expand Down Expand Up @@ -260,15 +271,15 @@ print(matches) # ['Apple', 'apple']

![Regular Expression cheat sheet](../images/regex.png)

Let's use examples to clarify the meta characters above
Let us use examples to clarify the meta characters above

### Square Bracket

Let's use square bracket to include lower and upper case
Let us use square bracket to include lower and upper case

```py
regex_pattern = r'[Aa]pple' # this square bracket mean either A or a
txt = 'Apple and banana are fruits. An old cliche says an apple a day a doctor way has been replaced by a banana a day keeps the doctor far far away. '
txt = 'Apple and banana are fruits. An old cliche says an apple a day a doctor way has been replaced by a banana a day keeps the doctor far far away.'
matches = re.findall(regex_pattern, txt)
print(matches) # ['Apple', 'apple']
```
Expand All @@ -277,7 +288,7 @@ If we want to look for the banana, we write the pattern as follows:

```py
regex_pattern = r'[Aa]pple|[Bb]anana' # this square bracket means either A or a
txt = 'Apple and banana are fruits. An old cliche says an apple a day a doctor way has been replaced by a banana a day keeps the doctor far far away. '
txt = 'Apple and banana are fruits. An old cliche says an apple a day a doctor way has been replaced by a banana a day keeps the doctor far far away.'
matches = re.findall(regex_pattern, txt)
print(matches) # ['Apple', 'banana', 'apple', 'banana']
```
Expand All @@ -288,18 +299,18 @@ Using the square bracket and or operator , we manage to extract Apple, apple, Ba

```py
regex_pattern = r'\d' # d is a special character which means digits
txt = 'This regular expression example was made on December 6, 2019.'
txt = 'This regular expression example was made on December 6, 2019 and revised on July 8, 2021'
matches = re.findall(regex_pattern, txt)
print(matches) # ['6', '2', '0', '1', '9'], this is not what we want
print(matches) # ['6', '2', '0', '1', '9', '8', '2', '0', '2', '1'], this is not what we want
```

### One or more times(+)

```py
regex_pattern = r'\d+' # d is a special character which means digits, + mean one or more times
txt = 'This regular expression example was made on December 6, 2019.'
txt = 'This regular expression example was made on December 6, 2019 and revised on July 8, 2021'
matches = re.findall(regex_pattern, txt)
print(matches) # ['6', '2019'] - now, this is better!
print(matches) # ['6', '2019', '8', '2021'] - now, this is better!
```

### Period(.)
Expand Down Expand Up @@ -332,34 +343,34 @@ Zero or one time. The pattern may not occur or it may occur once.

```py
txt = '''I am not sure if there is a convention how to write the word e-mail.
Some people write it email others may write it as Email or E-mail.'''
Some people write it as email others may write it as Email or E-mail.'''
regex_pattern = r'[Ee]-?mail' # ? means here that '-' is optional
matches = re.findall(regex_pattern, txt)
print(matches) # ['e-mail', 'email', 'Email', 'E-mail']
```

### Quantifier in RegEx

We can specify the length of the substring we are looking for in a text, using a curly bracket. Lets imagine, we are interested in a substring with a length of 4 characters:
We can specify the length of the substring we are looking for in a text, using a curly bracket. Let us imagine, we are interested in a substring with a length of 4 characters:

```py
txt = 'This regular expression example was made on December 6, 2019.'
txt = 'This regular expression example was made on December 6, 2019 and revised on July 8, 2021'
regex_pattern = r'\d{4}' # exactly four times
matches = re.findall(regex_pattern, txt)
print(matches) # ['2019']
print(matches) # ['2019', '2021']

txt = 'This regular expression example was made on December 6, 2019.'
txt = 'This regular expression example was made on December 6, 2019 and revised on July 8, 2021'
regex_pattern = r'\d{1, 4}' # 1 to 4
matches = re.findall(regex_pattern, txt)
print(matches) # ['6', '2019']
print(matches) # ['6', '2019', '8', '2021']
```

### Cart ^

* Starts with

```py
txt = 'This regular expression example was made on December 6, 2019.'
txt = 'This regular expression example was made on December 6, 2019 and revised on July 8, 2021'
regex_pattern = r'^This' # ^ means starts with
matches = re.findall(regex_pattern, txt)
print(matches) # ['This']
Expand All @@ -368,21 +379,23 @@ print(matches) # ['This']
* Negation

```py
txt = 'This regular expression example was made on December 6, 2019.'
txt = 'This regular expression example was made on December 6, 2019 and revised on July 8, 2021'
regex_pattern = r'[^A-Za-z ]+' # ^ in set character means negation, not A to Z, not a to z, no space
matches = re.findall(regex_pattern, txt)
print(matches) # ['6,', '2019.']
print(matches) # ['6,', '2019', '8', '2021']
```

## 💻 Exercises: Day 18

1. What is the most frequent word in the following paragraph?
### Exercises: Level 1
1. What is the most frequent word in the following paragraph?
```py
paragraph = 'I love teaching. If you do not love teaching what else can you love. I love Python if you do not love something which can give you all the capabilities to develop an application what else can you love.
```

```sh
[(6, 'love'),
[
(6, 'love'),
(5, 'you'),
(3, 'can'),
(2, 'what'),
Expand All @@ -403,18 +416,21 @@ print(matches) # ['6,', '2019.']
(1, 'an'),
(1, 'all'),
(1, 'Python'),
(1, 'If')]
(1, 'If')
]
```

2. The position of some particles on the horizontal x-axis -12, -4, -3 and -1 in the negative direction, 0 at origin, 4 and 8 in the positive direction. Extract these numbers from this whole text and find the distance between the two furthest particles.
2. The position of some particles on the horizontal x-axis are -12, -4, -3 and -1 in the negative direction, 0 at origin, 4 and 8 in the positive direction. Extract these numbers from this whole text and find the distance between the two furthest particles.

```py
points = ['-1', '2', '-4', '-3', '-1', '0', '4', '8']
sorted_points = [-4, -3, -1, -1, 0, 2, 4, 8]
distance = 12
distance = 8 -(-4) # 12
```

3. Write a pattern which identifies if a string is a valid python variable
### Exercises: Level 2

1. Write a pattern which identifies if a string is a valid python variable

```sh
is_valid_variable('first_name') # True
Expand All @@ -423,7 +439,9 @@ distance = 12
is_valid_variable('firstname') # True
```

4. Clean the following text. After cleaning, count three most frequent words in the string.
### Exercises: Level 3

1. Clean the following text. After cleaning, count three most frequent words in the string.

```py
sentence = '''%I $am@% a %tea@cher%, &and& I lo%#ve %tea@ching%;. There $is nothing; &as& mo@re rewarding as educa@ting &and& @emp%o@wering peo@ple. ;I found tea@ching m%o@re interesting tha@n any other %jo@bs. %Do@es thi%s mo@tivate yo@u to be a tea@cher!?'''
Expand Down

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