# Python3 Learning Notes

## by NCJ

<br />

<!-- `[TOC]` -->
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### Chapter 1 Setup


```python
import this
```

    The Zen of Python, by Tim Peters

    Beautiful is better than ugly.
    Explicit is better than implicit.
    Simple is better than complex.
    Complex is better than complicated.
    Flat is better than nested.
    Sparse is better than dense.
    Readability counts.
    Special cases aren't special enough to break the rules.
    Although practicality beats purity.
    Errors should never pass silently.
    Unless explicitly silenced.
    In the face of ambiguity, refuse the temptation to guess.
    There should be one-- and preferably only one --obvious way to do it.
    Although that way may not be obvious at first unless you're Dutch.
    Now is better than never.
    Although never is often better than *right* now.
    If the implementation is hard to explain, it's a bad idea.
    If the implementation is easy to explain, it may be a good idea.
    Namespaces are one honking great idea -- let's do more of those!


<br/>




### Chapter 2 Data Types

+ 001 variables


```python
msg = "hello"
print(msg)
```

    hello


 + 002 string operations


```python
name = "ada lovelace"
print(name.title())
print(name.upper())
print(name.lower())
```

    Ada Lovelace
    ADA LOVELACE
    ada lovelace



```python
new_msg = msg + " " + name
print ('\t' + new_msg + '\n')
```

    	hello ada lovelace




```python
msg_1 = '     hiuf yeb   w hviu ywe r         '
print(msg_1.rstrip())
```

         hiuf yeb   w hviu ywe r



```python
msg_1 = msg_1.rstrip()
print(msg_1.lstrip())
```

    hiuf yeb   w hviu ywe r



```python
msg_1 = '\t' + msg_1 + '\n'
print(msg_1)
msg_1 = msg_1.rstrip()
print(msg_1)
msg_1 = msg_1.lstrip()
print(msg_1)
```

    	     hiuf yeb   w hviu ywe r

    	     hiuf yeb   w hviu ywe r
    hiuf yeb   w hviu ywe r


+ 003 number operations


```python
10**6
```




    1000000




```python
3/2
```




    1.5




```python
3//2
```




    1




```python
0.1*3
```




    0.30000000000000004



*floats' problems still exists in python3, but it's common in any language due to how computers save these floats*

+ 004 number&string


```python
num_test_1 = 666
print(num_test_1)
    # print('huvife' + num_test_1 + 'gbtehgbe')
    # error version
print('huvife' + str(num_test_1) + 'gbtehgbe')
    # or
num_test_1 = '666'
print('huvife' + num_test_1 + 'gbtehgbe')
```

    666
    huvife666gbtehgbe
    huvife666gbtehgbe


<br/>

### Chapter 3 List

*There is no array in Python!!!*

+ 001 Introduction to Lists


```python
arr = ['vfervewr','gftewgwter','gtewgewwe','gtwgw']
print(arr)
print(arr[0].title())
print(arr[-1]) #see? minus is not only available, but useful!
print(arr[-3])
message = "vfsvegeerwsgetrw " + arr[0] + " vbgfdbgfrdsbg"
print(message)
    # message = "vfsvegeerwsgetrw " + arr + " vbgfdbgfrdsbg"
    # print(message)
    # error version
```

    ['vfervewr', 'gftewgwter', 'gtewgewwe', 'gtwgw']
    Vfervewr
    gtwgw
    gftewgwter
    vfsvegeerwsgetrw vfervewr vbgfdbgfrdsbg


&emsp;&emsp;*Again, thers is no array in Python! So don't follow my mistake! (I used 'arr' to name a list, because I thought they were the same!)*

+ 002 Modifying Lists


```python
arr[0] = 'cool'
print(arr)
```

    ['cool', 'gftewgwter', 'gtewgewwe', 'gtwgw']


+ 003 Add Elements


```python
arr.append('new one')
print(arr)
```

    ['cool', 'gftewgwter', 'gtewgewwe', 'gtwgw', 'new one']


&emsp;&emsp;You can even create an empty list and add elements to it later!


```python
motor = []

motor.append('honda')
motor.append('yamaha')
motor.append('suzuki')

print(motor)
```

    ['honda', 'yamaha', 'suzuki']


+ 004 Insert Elements


```python
motor.insert(0,'ducati')
print(motor)
```

    ['ducati', 'honda', 'yamaha', 'suzuki']


+ 005 Delete Elements


```python
print(motor)

del motor[1]
print(motor)
```

    ['ducati', 'honda', 'yamaha', 'suzuki']
    ['ducati', 'yamaha', 'suzuki']


+ 006 Pop Elements


```python
print(motor)

poped_motor = motor.pop()
print(motor)
print(poped_motor)
```

    ['ducati', 'yamaha', 'suzuki']
    ['ducati', 'yamaha']
    suzuki


&emsp;&emsp;This way, you can still use the element you want to delete for the last time.
&emsp;&emsp;This is useful! Watch this example!


```python
motor = ['ducati', 'honda', 'yamaha', 'suzuki']

last_owned = motor.pop()
print("The last motorcycle I owned was a " + last_owned.title() + ".")
print(motor)
```

    The last motorcycle I owned was a Suzuki.
    ['ducati', 'honda', 'yamaha']


&emsp;&emsp;And pop can be used to pop any element!


```python
motor = ['ducati', 'honda', 'yamaha', 'suzuki']

first_owned = motor.pop(0)
print("The first motorcycle I owned was a " + first_owned.title() + ".")
print(motor)
```

    The first motorcycle I owned was a Ducati.
    ['honda', 'yamaha', 'suzuki']


+ 007 Remove Elements According to Its Value


```python
motor = ['ducati', 'honda', 'yamaha', 'suzuki']

motor.remove('ducati')
print(motor)
```

    ['honda', 'yamaha', 'suzuki']



```python
motor = ['ducati', 'honda', 'yamaha', 'suzuki']

too_expensive = 'ducati'
motor.remove(too_expensive)
print(motor)
print("\nA " + too_expensive.title() + " is too expensive for me.")
```

    ['honda', 'yamaha', 'suzuki']

    A Ducati is too expensive for me.