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Python Getting Started

資料來源

Complete-Python-3-Bootcamp @ GitHub

Setup & Installation​

Anaconda​

# 關掉 Anaconda 自動在 Terminal 中啟動 base environment "(base)"
$ conda config --set auto_activate_base false

# 啟動 Anaconda
$ conda activate

Data Structure Basic​

Variable​

a = 3
type(a) # int

String​

參考資料
##
# Index and Slice
##
'tinker'[1:4]   # 'ink'
'tinker'[1:4:2] # 'ik'
'tinker'[::-1]  # 'reknit

##
# Formatting with the .format() method
##
'Good {}, {} Chen!'.format('morning', 'Mr.') # 'Good morning, Mr. Chen!'
'My favorite brand is {}, {}, and {}!'.format('Apple', 'Samsung', 'Google') # 'My favorite brand is Apple, Samsung, and Google!'
'My favorite brand is {2}, {1}, and {0}!'.format('Apple', 'Samsung', 'Google') # 'My favorite brand is Google, Samsung, and Apple!'

'Repeat after me: {0}! {0}! {0}!'.format('Ho') # 'Repeat after me: Ho! Ho! Ho!'
'Good {time}, {title} {name}!'.format(time='morning', title='Mr.', name='Chen') # 'Good morning, Mr. Chen!'

##
# Float Formatting
##
result = 100/777  # 0.1287001287001287

# Old Way, {value:width.precision f}
print("The result was {:1.3f}".format(result))  # The result was 0.129

# Formatted String Literals(f-strings)
name = 'Aaron'
age = 33
print(f'Hello, my name is {name}, and I\'m {age} years old.')

List​

[0]*3  # [0, 0, 0]

my_list = [1, 3, 2]
another_list = [4, 6, 5]

# array concat
whole_list = my_list + another_list
whole_list  # [1, 3, 2, 4, 6, 5]

# sort
whole_list.sort()
whole_list  # [1, 2, 3, 4, 5, 6]
whole_list.reverse()
whole_list  # [6, 5, 4, 3, 2, 1]

Operators​

Comparisons Operators​

1 < 2 < 3  # True
1 < 2 and 2 < 3 # True
1 == 1 or 2 == 2 # True
not ( 1 == 1 ) # False
not ( 400 > 5000 ) # True

Useful Operators​

range(start, stop, step)​

# 0, 1, 2
for i in range(3):
    print(i)

# 3, 4
for i in range(3,5):
    print(i)

# 1,3,5
for i in range(1,6,2):
    print(i)

# [0, 2, 4]
list(range(0, 5, 2))

enumerator​

把 string 變成 tuple

word = 'abc'

# 0: a
# 1: b
# 2: c
for idx, value in enumerate(word):
    print(f'{idx}: {value}')

zip​

把多個 list 組成一個 tuple

name = ['Aaron', 'John', 'Mary']
age = [12, 13, 14]
height = [170, 180, 160]

# Aaron is 12 years old with 170 cm
# John is 13 years old with 180 cm
# Mary is 14 years old with 160 cm
for name, age, height in zip(name, age, height):
    print(f'{name} is {age} years old with {height} cm')

# <zip object at 0x1023a1300>
zip(name, age, height)

# [('Aaron', 12, 170), ('John', 13, 180), ('Mary', 14, 160)]
list(zip(name, age, height))

in​

1 in [1, 2, 3]  # True

'a' in 'abc'  # True
'a' in [1, 2, 3]  # False

user = {
    "name": "John",
    "age": 30,
    "city": "New York"
}
'name' in user # True
'John' in user.values()

Statements​

Conditional Statements​

state = 'active'

if state == 'active':
    print('The state is active')
elif state == 'inactive':
    print('The state is inactive')
else:
    print('The state is unknown')

For Loops​

Iterate a list​

brands = ['Ford', 'BMW', 'Volvo']
for brand in brands:
    print(brand)

Combine with conditional statement:

brands = ['Ford', 'BMW', 'Volvo']
for brand in brands:
    if brand == 'Volvo':
        print(brand + ' - I like it!')
    else:
        print(brand + ' - I don\'t like it!')

Iterate a string​

str = 'Hello World'
for letter in str:
    print(letter)

Iterate a tuple​

for t in (1, 2, 3):
    print(t)

Tuple Unpacking​

my_list = [(1, 2), (3, 4), (5, 6), (7, 8), (9, 10)]

for a, b in my_list:
    print(a + b)

Iterate an dictionary​

user = {
    "name": "John",
    "age": 30,
    "city": "New York"
}

for key in user:
    print(f'key: {key}')
    print(f'value: {user[key]}')

for key, value in user.items():
    print(f'key: {key}')
    print(f'value: {value}')

for value in user.values():
    print(value)

While Loops​

x = 0
while x < 5:
    # x = x + 1
    x += 1
    print(f'The current value of x is {x}')
# could combine with "else"
else:
    print('X IS NOT LESS THAN 5')

Basic I/O​

Read and Write files​

  • mode='r': read only
  • mode='w': write only (will overwrite existing files or create new)
  • mode='a': append only
  • mode='r+': read and write
  • mode='w+': write and read (overwrite existing files or create new)
myfile = open('myfile.txt')
myfile.read()
myfile.seek(0)  # reset cursor
myfile.readlines()  # returns a list of lines
myfile.close()  # close file

# 不用怕忘記 close 的寫法
# create or overwrite a file
with open('myfile.txt', mode="w") as my_new_file:
    contents = my_new_file.write(
        'this is a text file\nthis is the second line\nthis is the third line')

# read file
with open('myfile.txt', mode='r') as f:
    contents = f.read()
    print(contents)

# append file
with open('myfile.txt', mode='a') as f:
    f.write('\nthis is the fourth line')

with open('myfile.txt', mode='r') as f:
    contents = f.read()
    print(contents)