Python Basic #

$ python --version
Python 2.7.16
$ which python
/usr/bin/python

$ brew update
$ brew install python

$ vi ~/.bash_profile
export PATH="/usr/local/opt/python/libexec/bin:$PATH"
$ source ~/.bash_profile

$ python --version
Python 3.9.13
$ which python
/usr/local/opt/python/libexec/bin/python

$ brew update
$ brew upgrade python

$ python --version
Python 3.9.13

$ python -V
Python 3.9.13

$ python -VV
Python 3.9.13 (main, May 24 2022, 21:28:31)
[Clang 13.1.6 (clang-1316.0.21.2)]

$ python
>>> print("Hi", "Mike")
Hi Mike
>>> print("Hi", "Mike", sep=", ", end=".\n")
Hi, Mike.
>>> 2 + 2
4
>>> type(1)
<class 'int'>
>>> type(1.0)
<class 'float'>
>>> .1
0.1
>>> 17 / 2
8.5
>>> 17 / 5
3.4
>>> 19 / 3
6.333333333333333
>>> 19 // 3
6
>>> 4 * 4 * 4
64
>>> 4 ** 3
64
>>> pie = 3.14159265359
>>> pie
3.14159265359
>>> round(pie, 2)
3.14
>>> import math
>>> math.sqrt(25)
5.0
>>> help(math)

$ python
>>> print('c:\name')
c:
ame
>>> print('c:\\name')
c:\name
>>> print(r'c:\name')
c:\name
>>> print("""
... aaa
... bbb
... ccc
... """)

aaa
bbb
ccc

>>>
>>> print('Hello, ' * 2 + 'Mark')
Hello, Hello, Mark
>>> str = ('aaaaaa''bbbbbb')
>>> str
'aaaaaabbbbbb'
>>> str = ('aaaaaa'
... 'bbbbbb')
>>> str
'aaaaaabbbbbb'
>>> 
>>> str = 'python'
>>> str[0]
'p'
>>> str[1]
'y'
>>> str[2]
't'
>>> str[-1]
'n'
>>> str[0:2]
'py'
>>> str[:2]
'py'
>>> str[2:]
'thon'
>>> 'J' + str[1:]
'Jython'
>>> str[:]
'Jython'
>>> n = len(str)
>>> n
6
>>> 
>>> s = 'My name is Alice. Hi, Alice.'
>>> s
'My name is Alice. Hi, Alice.'
>>> 
>>> is_start = s.startswith('My')
>>> is_start
True
>>> 
>>> s.find('Alice')
11
>>> 
>>> s.rfind('Alice')
22
>>> 
>>> s.count('Alice')
2
>>> 
>>> s.capitalize()
'My name is alice. hi, alice.'
>>> 
>>> s.title()
'My Name Is Alice. Hi, Alice.'
>>> 
>>> s.upper()
'MY NAME IS ALICE. HI, ALICE.'
>>> 
>>> s.lower()
'my name is alice. hi, alice.'
>>> 
>>> s.replace('Alice', 'Bob')
'My name is Bob. Hi, Bob.'
>>> 
>>> 'My name is {}.'.format('Chris')
'My name is Chris.'
>>> 
>>> "My name is {}. I'm a {}.".format('Chris', 'student')
"My name is Chris. I'm a student."
>>>
>>> "My family name is {1}, my first name is {0}.".format('John', 'Smith')
'My family name is Smith, my first name is John.'
>>> 
>>> "My family name is {family_name}, my first name is {first_name}.".format(first_name='John', family_name='Smith')
'My family name is Smith, my first name is John.'
>>>
>>> x = str(1)
>>> type(x)
<class 'str'>
>>> 
>>> first_name = 'John'
>>> family_name = 'Smith'
>>> print(f'My name is {first_name} {family_name}.')
My name is John Smith.
>>> 

$ python
>>> l = [1, 20, 300, 4000, 50000]
>>> l[0]
1
>>> l[1]
20
>>> l[-1]
50000
>>> l[0:2]
[1, 20]
>>> l[2:4]
[300, 4000]
>>> l[2:]
[300, 4000, 50000]
>>> l[:]
[1, 20, 300, 4000, 50000]
>>> len(l)
5
>>> type(l)
<class 'list'>
>>> 
>>> list('abc')
['a', 'b', 'c']
>>> l = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> l[::2]
[1, 3, 5, 7, 9]
>>> l[1::2]
[2, 4, 6, 8, 10]
>>> l[::-1]
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
>>> x = ['a', 'b', 'c']
>>> y = ['e', 'f', 'g']
>>> z = [x, y]
>>> z
[['a', 'b', 'c'], ['e', 'f', 'g']]
>>> z[0]
['a', 'b', 'c']
>>> z[0][0]
'a'
>>> z[1][2]
'g'
>>> zz = x + y
>>> zz
['a', 'b', 'c', 'e', 'f', 'g']
>>> 

import sys

print(sys.version)
# Python 3.9.13 (main, May 24 2022, 21:28:31)
# [Clang 13.1.6 (clang-1316.0.21.2)]
print(type(sys.version))
# <class 'str'>

print(sys.version_info)
# sys.version_info(major=3, minor=9, micro=13, releaselevel='final', serial=0)
print(type(sys.version_info))
# <class 'sys.version_info'>

print(sys.version_info[0])
# 3
print(sys.version_info[1])
# 9
print(sys.version_info[2])
# 13

print(sys.version_info.major)
# 3
print(sys.version_info.minor)
# 9
print(sys.version_info.micro)
# 13

import platform

print(platform.python_version())
# 3.9.13
print(type(platform.python_version()))
# <class 'str'>
print(platform.python_version_tuple())
# ('3', '9', '13')
print(type(platform.python_version_tuple()))
# <class 'tuple'>

$ pip list

$ pip freeze

$ pip show <installed package>

$ pip show numpy

import sys

args = sys.argv

print(args)
print(args[1])
print(args[2])

$ python simple.py aaa 123
['sample.py', 'aaa', '123']
aaa

import argparse

description = 'A description of this program.'
parser = argparse.ArgumentParser(description=description)
parser.add_argument('foo', type=str, help='First argument.')
parser.add_argument('bar', type=int, help='Second argument.')
args = parser.parse_args()

print(args)
print(args.foo)
print(args.bar)

$ python sample.py aaa 123
Namespace(foo='aaa', bar=123)
aaa
123

$ python sample.py --help
usage: sample.py [-h] foo bar

A description of this program.

positional arguments:
  foo         First argument.
  bar         Second argument.

optional arguments:
  -h, --help  show this help message and exit

import argparse

description = 'A description of this program.'
parser = argparse.ArgumentParser(description=description)

help = 'A required named argument.'
parser.add_argument('--named_arg1', type=str, required=True, help=help)

help = 'An optional named argument.'
parser.add_argument('--named_arg2', type=int, help=help)

help = 'True is specified automatically if you set this.'
parser.add_argument('--flag1', action='store_true', help=help)

help = 'False is specified automatically if you set this.'
parser.add_argument('--flag2', action='store_false', help=help)

args = parser.parse_args()

print(args)

print(args.named_arg1)
print(args.named_arg2)
print(args.flag1)
print(args.flag2)

$ python sample.py --named_arg1 aaa --named_arg2 123 --flag1 --flag2
Namespace(named_arg1='aaa', named_arg2=123, flag1=True, flag2=False)
aaa
123
True
False

import os
os.getcwd()

import os
absolute_path = os.path.abspath(path)

import os
os.path.isabs(path)

import os
relative_path = os.path.relpath(path)

import os
dir_name = os.path.dirname(file_path)

import os
file_name = os.path.basename(file_path)

import os
file_stem = os.path.splitext(file_name)[0] # sample.png -> sample

import os
path = "/foo/bar/sample.png"
os.path.exists(path)

import os
path = "/foo/bar/sample.png"
os.path.isfile(path)

import os
path = "/foo/bar/"
os.path.isdir(path)