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04_Day_Strings/04_strings.md
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@ -9,10 +9,9 @@
<sub>Author:
<a href="https://www.linkedin.com/in/asabeneh/" target="_blank">Asabeneh Yetayeh</a><br>
<small> First Edition: Nov 22 - Dec 22, 2019</small>
<small> Second Edition: July, 2021</small>
</sub>
</div>
</div>
[<< Day 3](../03_Day_Operators/03_operators.md) | [Day 5 >>](../05_Day_Lists/05_lists.md)
@ -24,9 +23,9 @@
- [Creating a String](#creating-a-string)
- [String Concatenation](#string-concatenation)
- [Escape Sequences in Strings](#escape-sequences-in-strings)
- [String formating](#string-formating)
- [Old Style String Formating (% Operator)](#old-style-string-formating--operator)
- [New Style String Formating (str.format)](#new-style-string-formating-strformat)
- [String formatting](#string-formatting)
- [Old Style String Formatting (% Operator)](#old-style-string-formatting--operator)
- [New Style String Formatting (str.format)](#new-style-string-formatting-strformat)
- [String Interpolation / f-Strings (Python 3.6+)](#string-interpolation--f-strings-python-36)
- [Python Strings as Sequences of Characters](#python-strings-as-sequences-of-characters)
- [Unpacking Characters](#unpacking-characters)
@ -41,7 +40,7 @@
## Strings
Text is a string data type. Any data type written as text is a string. Any data under single or double quote are strings. There are different string methods and built-in functions to deal with string data types. To check the length of a string use the len() method.
Text is a string data type. Any data type written as text is a string. Any data under single, double or triple quote are strings. There are different string methods and built-in functions to deal with string data types. To check the length of a string use the len() method.
### Creating a String
@ -49,20 +48,21 @@ Text is a string data type. Any data type written as text is a string. Any data
letter = 'P' # A string could be a single character or a bunch of texts
print(letter) # P
print(len(letter)) # 1
greeting = 'Hello, World!' # String could be a single or double quote,"Hello, World!"
greeting = 'Hello, World!' # String could be made using a single or double quote,"Hello, World!"
print(greeting) # Hello, World!
print(len(greeting)) # 13
sentence = "I hope you are enjoying 30 days of Python Challenge"
print(sentence)
```
Multiline string is created by using triple single (''') or double quotes ("""). See the example below.
Multiline string is created by using triple single (''') or triple double quotes ("""). See the example below.
```py
multiline_string = '''I am a teacher and enjoy teaching.
I didn't find anything as rewarding as empowering people.
That is why I created 30 days of python.'''
print(multiline_string)
# Another way of doing the same thing
multiline_string = """I am a teacher and enjoy teaching.
I didn't find anything as rewarding as empowering people.
@ -80,7 +80,7 @@ last_name = 'Yetayeh'
space = ' '
full_name = first_name + space + last_name
print(full_name) # Asabeneh Yetayeh
# Checking length of a string using len() built-in function
# Checking the length of a string using len() built-in function
print(len(first_name)) # 8
print(len(last_name)) # 7
print(len(first_name) > len(last_name)) # True
@ -89,7 +89,7 @@ print(len(full_name)) # 16
### Escape Sequences in Strings
In python and other programming languages \ followed by a character. Let's see the most common escape characters:
In Python and other programming languages \ followed by a character is an escape sequence. Let us see the most common escape characters:
- \n: new line
- \t: Tab means(8 spaces)
@ -97,15 +97,17 @@ In python and other programming languages \ followed by a character. Let's see t
- \\': Single quote (')
- \\": Double quote (")
Now, let us see the use of the above escape sequences with examples.
```py
print('I hope everyone is enjoying the Python Challenge.\nAre you ?') # line break
print('Days\tTopics\tExercises')
print('Days\tTopics\tExercises') # adding tab space or 4 spaces
print('Day 1\t3\t5')
print('Day 2\t3\t5')
print('Day 3\t3\t5')
print('Day 4\t3\t5')
print('This is a backslash symbol (\\)') # To write a backslash
print('In every programming language it starts with \"Hello, World!\"')
print('In every programming language it starts with \"Hello, World!\"') # to write a double quote inside a single quote
# output
I hope every one is enjoying the Python Challenge.
@ -119,17 +121,17 @@ This is a backslash symbol (\)
In every programming language it starts with "Hello, World!"
```
### String formating
### String formatting
#### Old Style String Formating (% Operator)
#### Old Style String Formatting (% Operator)
In python there are many ways of formating strings. In this section we will cover some of them.
The "%" operator is used to format a set of variables enclosed in a "tuple" (a fixed size list), together with a format string, which contains normal text together with "argument specifiers", special symbols like "%s", "%d", "%f", "%.<number of digits>f".
In Python there are many ways of formatting strings. In this section, we will cover some of them.
The "%" operator is used to format a set of variables enclosed in a "tuple" (a fixed size list), together with a format string, which contains normal text together with "argument specifiers", special symbols like "%s", "%d", "%f", "%.<small>number of digits</small>f".
- %s - String (or any object with a string representation, like numbers)
- %d - Integers
- %f - Floating point numbers
- %.<number of digits>f - Floating point numbers with fixed precision
- "%.<small>number of digits</small>f" - Floating point numbers with fixed precision
```py
# Strings only
@ -145,14 +147,14 @@ pi = 3.14
area = pi * radius ** 2
formated_string = 'The area of circle with a radius %d is %.2f.' %(radius, area) # 2 refers the 2 significant digits after the point
python_libraries = ['Django', 'Flask', 'Numpy', 'Pandas']
python_libraries = ['Django', 'Flask', 'NumPy', 'Matplotlib','Pandas']
formated_string = 'The following are python libraries:%s' % (python_libraries)
print(formated_string) # "The following are python libraries:['Django', 'Flask', 'Numpy', 'Pandas']"
print(formated_string) # "The following are python libraries:['Django', 'Flask', 'NumPy', 'Matplotlib','Pandas']"
```
#### New Style String Formating (str.format)
#### New Style String Formatting (str.format)
This formating is introduced in python version 3.
This formatting is introduced in Python version 3.
```py
@ -185,14 +187,14 @@ print('{} ** {} = {}'.format(a, b, a ** b))
radius = 10
pi = 3.14
area = pi * radius ** 2
formated_string = 'The area of a cricle with a radius {} is {:.2f}.'.format(radius, area) # 2 digits after decimal
formated_string = 'The area of a circle with a radius {} is {:.2f}.'.format(radius, area) # 2 digits after decimal
print(formated_string)
```
#### String Interpolation / f-Strings (Python 3.6+)
Another new string formating is string interpolation, f-strings. Strings start with f and we can inject the data in their corresponding positions.
Another new string formatting is string interpolation, f-strings. Strings start with f and we can inject the data in their corresponding positions.
```py
a = 4
@ -257,6 +259,7 @@ In python we can slice strings into substrings.
```py
language = 'Python'
first_three = language[0:3] # starts at zero index and up to 3 but not include 3
print(first_three) #Pyt
last_three = language[3:6]
print(last_three) # hon
# Another way
@ -281,7 +284,7 @@ It is possible to skip characters while slicing by passing step argument to slic
```py
language = 'Python'
pto = language[0,6:2] #
pto = language[0:6:2] #
print(pto) # Pto
```
@ -289,19 +292,19 @@ print(pto) # Pto
There are many string methods which allow us to format strings. See some of the string methods in the following example:
- capitalize(): Converts the first character of the string to capital Letter
- capitalize(): Converts the first character of the string to capital letter
```py
challenge = 'thirty days of python'
print(challenge.capitalize()) # 'Thirty days of python'
```
- count(): returns occurrences of substring in string, count(substring, start=.., end=..)
- count(): returns occurrences of substring in string, count(substring, start=.., end=..). The start is a starting indexing for counting and end is the last index to count.
```py
challenge = 'thirty days of python'
print(challenge.count('y')) # 3
print(challenge.count('y', 7, 14)) # 1
print(challenge.count('y', 7, 14)) # 1,
print(challenge.count('th')) # 2`
```
@ -321,7 +324,7 @@ print(challenge.expandtabs()) # 'thirty days of python'
print(challenge.expandtabs(10)) # 'thirty days of python'
```
- find(): Returns the lowest index of the first occurrence of a substring, if not found returns -1
- find(): Returns the index of the first occurrence of a substring, if not found returns -1
```py
challenge = 'thirty days of python'
@ -329,7 +332,7 @@ print(challenge.find('y')) # 5
print(challenge.find('th')) # 0
```
- rfind(): Returns the highest index of the first occurrence of a substring, if not found returns -1
- rfind(): Returns the index of the last occurrence of a substring, if not found returns -1
```py
challenge = 'thirty days of python'
@ -338,15 +341,16 @@ print(challenge.find('th')) # 1
```
- format(): formats string into a nicer output
More about string formating check this [link](https://www.programiz.com/python-programming/methods/string/format)
More about string formatting check this [link](https://www.programiz.com/python-programming/methods/string/format)
```py
first_name = 'Asabeneh'
last_name = 'Yetayeh'
age = 250
job = 'teacher'
country = 'Finland'
sentence = 'I am {} {}. I am a {}. I live in {}.'.format(first_name, last_name, job, country)
print(sentence) # I am Asabeneh Yetayeh. I am a teacher. I live in Finland.
sentence = 'I am {} {}. I am a {}. I am {} years old. I live in {}.'.format(first_name, last_name, age, job, country)
print(sentence) # I am Asabeneh Yetayeh. I am 250 years old. I am a teacher. I live in Finland.
radius = 10
pi = 3.14
@ -435,7 +439,7 @@ num = '10.5'
print(num.isnumeric()) # False
```
- isidentifier(): Checks for a valid identifier - means it checks, if a string is a valid variable name
- isidentifier(): Checks for a valid identifier - it checks if a string is a valid variable name
```py
challenge = '30DaysOfPython'
@ -464,13 +468,19 @@ print(challenge.isupper()) # True
- join(): Returns a concatenated string
```py
web_tech = ['HTML', 'CSS', 'JavaScript', 'React']
result = ' '.join(web_tech)
print(result) # 'HTML CSS JavaScript React'
```
```py
web_tech = ['HTML', 'CSS', 'JavaScript', 'React']
result = '# '.join(web_tech)
print(result) # 'HTML# CSS# JavaScript# React'
```
- strip(): Removes all given characters starting from the beggining and end of the string
- strip(): Removes all given characters starting from the beginning and end of the string
```py
challenge = 'thirty days of pythoonnn'
@ -484,7 +494,7 @@ challenge = 'thirty days of python'
print(challenge.replace('python', 'coding')) # 'thirty days of coding'
```
- split(): Splits the string, using given string as a separator
- split(): Splits the string, using given string or space as a separator
```py
challenge = 'thirty days of python'
@ -519,7 +529,7 @@ challenge = '30 days of python'
print(challenge.startswith('thirty')) # False
```
🌕 You are extraordinary and you have a remarkable potential. You have just completed day 4 challenges and you are four steps a head in to your way to greatness. Now do some exercises for your brain and for your muscle.
🌕 You are an extraordinary person and you have a remarkable potential. You have just completed day 4 challenges and you are four steps a head in to your way to greatness. Now do some exercises for your brain and muscles.
## 💻 Exercises - Day 4
@ -528,7 +538,7 @@ print(challenge.startswith('thirty')) # False
3. Declare a variable named company and assign it to an initial value "Coding For All".
4. Print the variable company using _print()_.
5. Print the length of the company string using _len()_ method and _print()_.
6. Change all the characters to capital letters using _upper()_ method.
6. Change all the characters to uppercase letters using _upper()_ method.
7. Change all the characters to lowercase letters using _lower()_ method.
8. Use capitalize(), title(), swapcase() methods to format the value of the string _Coding For All_.
9. Cut(slice) out the first word of _Coding For All_ string.
@ -564,18 +574,18 @@ print(challenge.startswith('thirty')) # False
```
34. Use a tab escape sequence to write the following lines.
```py
Name Age Country
Asabeneh 250 Finland
Name Age Country City
Asabeneh 250 Finland Helsinki
```
35. Use the string formating method to display the following:
35. Use the string formatting method to display the following:
```sh
radius = 10
area = 3.14 * radius ** 2
The area of a cricle with radius 10 is 314 meters square.
The area of a circle with radius 10 is 314 meters square.
```
36. Make the following using string formating methods:
36. Make the following using string formatting methods:
```sh
8 + 6 = 14