Python Base Info

Terms

High-level language and program written in C that interprets the source code, parses it (examine/analyze syntactic structure) and processes it
semantic: meaning of a prog.
syntax: rules that define the structure of the lang.
Translator types:
1. interpreters: executes prog. in high level lang by translating 1 line at a time
2. compilers: get's the prog. file, then runs a process to translate the high-level source code into machine language; afterwards it puts it into a file to be executed later in .exe or .dll files (executable and dynamic link library)
3. machine code/low-level lang/assembly lang: the lowest level lang. for software that's directly executed by CPU
programs (py statements crafted to do a task) are saved to files called scripts and called by running: python <filename.py>
variable: a name that refers to a value. An assignment statement creates new var and gives them values
attribute: a value associated w/ an object; referenced by using dot expression/notation (candy.sour)
callback: subroutine func passed as an arg. to be ee in future
class: a temp for making user-defined objects. Contain method def. that operate on instances of the class
coercion: implicit conversion of one type to another that involves 2 args of same type
decorator: function returning another func. (func transformation using @wrapper syntaxl ex. classmethod(), staticmethod())
descriptor: Any object which defines the methods get(), set(), or delete()
dictionary comprehension: A compact way to process all or part of the elements in an iterable and return a dictionary with the results.
dictionary view: The objects returned from dict.keys(), dict.values(), and dict.items() are called dictionary views.
generator: A function which returns a generator iterator. It looks like a normal function except that it contains yield expressions for producing a series of values usable in a for-loop or that can be retrieved one at a time with the next() function.
immutable: An object with a fixed value. Immutable objects include numbers, strings and tuples. Such an object cannot be altered
Mutable objects can change their value but keep their id().
type: The type of a Python object determines what kind of object it is; every object has a type. An object’s type is accessible as its class attribute or can be retrieved with type(obj).

To-Do

iterable An object capable of returning its members one at a time. Examples of iterables include all sequence types (such as list, str, and tuple) and some non-sequence types like dict, file objects, and objects of any classes you define with an iter() method or with a getitem() method that implements Sequence semantics.
iterator An object representing a stream of data. Repeated calls to the iterator’s next() method (or passing it to the built-in function next()) return successive items in the stream.
key function A key function or collation function is a callable that returns a value used for sorting or ordering. For example, locale.strxfrm() is used to produce a sort key that is aware of locale specific sort conventions. A number of tools in Python accept key functions to control how elements are ordered or grouped. They include min(), max(), sorted(), list.sort(), heapq.merge(), heapq.nsmallest(), heapq.nlargest(), and itertools.groupby().

a.list

A built-in Python sequence. Despite its name it is more akin to an array in other languages than to a linked list
- since access to elements is O(1)
an ordered set of items

a_list = ['a']
a_list[:] # creates copy of the list
a_l = a_l + [2.0, 3]
a_l.append('dog')
a_l.extend()

list comprehension A compact way to process all or part of the elements in a sequence and return a list with the results.

 result = ['{:#04x}'.format(x) for x in range(256) if x % 2 == 0]
"""
 generates a list of strings containing even hex numbers (0x..) in the range  0 - 255.
 The if clause is optional. If omitted, all elements in range(256) are processed.
"""

mapping A container object that supports arbitrary key lookups and implements the methods specified in the Mapping or MutableMapping abstract base classes. Examples include dict, collections.defaultdict, collections.OrderedDict and collections.Counter.
method A function which is defined inside a class body. If called as an attribute of an instance of that class, the method will get the instance object as its first argument (which is usually called self).
sequence An iterable which supports efficient element access using integer indices via the getitem() special method and defines a len() method that returns the length of the sequence. Some built-in sequence types are list, str, tuple, and bytes. Container w/ items stored in deterministic ordering
set comprehension A compact way to process all or part of the elements in an iterable and return a set with the results. results = {c for c in 'abracadabra' if c not in 'abc'} generates the set of strings {'r', 'd'}

def f(arg):
    ...
f = staticmethod(f)

@staticmethod
def f(arg):
    ...

(int(3.15)) # converts floating pt # to integer 3

Argument passing

script name and add'l args are turned into a list of str then assigned to argv var. in sys module
Shebang lines
file starts with #!
Linux/Unix OS have native support and the py launcher allows use with Py scripts on W10.
virtual commands include

/usr/bin/env python, /usr/bin/python, /usr/local/bin/python, python

#! /usr/bin/python || usr/bin/python -v || ./.myvenv/Scripts/python.exe

virtual env creation

python3 -m venv /path/to/new/virtual/environment
c:/Python35/python -m venv c:/path/to/myenv
python -m venv c:/path/to/myenv
python -m venv -h
<venv>\Scripts\Activate.ps1
venv/Scripts/Activate.ps1
<venv>/bin/Activate.ps1
venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
            [--upgrade] [--without-pip] [--prompt PROMPT] [--upgrade-deps]
            ENV_DIR [ENV_DIR ...]

source <venv>/bin/activate
venv\/Scripts\/activate.bat
venv\/Scripts\/activate.bat

source "c:/Users/uname/OneDrive -PPU/uname @PPU/moons/.venv/Scripts/activate"
source /home/uname/flow/work/.venv/bin/activate

positional args: ENV_DIR: a dir to create the environment in.
optional args
-h || --help
--system-site-packages (give access to system site-pack dir.)
--symlinks
--copies
--clear (delete contents of the env dir before creation)
--upgrade (upgrade env dir to use newer v of py)
--upgrade-deps (upgrade cored deps & pip setuptools)
--prompt PROMPT (set an alt prompt prefix for the env)

python -m pip install wheel
python -m pip wheel --wheel-dir=/local/wheels -r requirements.txt
# build wheels for your requirements and all their dependencies to a local directory:
python -m pip install --no-index --find-links=/local/wheels -r requirements.txt
# install those requirements just using your local directory of wheels
python -m pip wheel --wheel-dir=/tmp/wheelhouse SomePackage
python -m pip install --no-index --find-links=/tmp/wheelhouse SomePackage
# Build wheels for a requirement (and all its dependencies), and then **install**
pip install --upgrade --upgrade-strategy eager --report ./PipRep.json --cache-dir ./.venv/pip_cache -r ./requirements.txt
pip install --require-virtualenv --upgrade --upgrade-strategy=eager --no-binary=:all: --dry-run --ignore-installed -r ./requirements.txt

pip install --require-virtualenv --python-version "3.10.0" --pre --upgrade
# only install in venv, use py -v, use pre-release -v, upgrade packages (-u), isolated mode ignores env var and user config
# --user Install to the Python user install dir Linux: ~/.local/, or W10:%APPDATA%\Python

# ERROR: When restricting platform and interpreter constraints using --python-version, --platform, --abi, or --implementation,
    # either --no-deps must be set, or --only-binary=:all: must be set and --no-binary must not be set (or must be set to :none:).
pip install --python "3.8"
#  run w/ specified python interpreter
pip install --dry-run --ignore-installed
# don't install and resolve the requirements, can use --report <file_name> to check what pip did to install req
pip install -r requirements.txt
pip install --use-feature no-binary-enable-wheel-cache truststore fast-deps
pip cache <dir, info, list, purge, remove>
pip config # (debug, edit, get, list, set, unset)
python3 -m pip install --upgrade flake8 autopep8 --upgrade-strategy=eager
pip install --upgrade SomePackage --upgrade-strategy=eager
# upgrade pack to latest
--no-binary <format_control> ":all:" # don't use legacy binary packs
--no-deps # don't install deps
--use-pep517  # Use PEP 517 for building source distributions
--compile # compile/don't compile Py source fi to bytecode
--check-build-dependencies  # Check the build dependencies when PEP517 is used.
--config-settings <KEY=VALUE>
pushd "$(mktemp -d)"
time python -m pip install \
      --no-cache-dir \
      --force-reinstall \
      --only-binary=cryptography \
      cryptography
# curl
curl --dns-servers 1.1.1.1,1.0.0.1 --compressed -o $file -# $url

Pip commands

Commands	info
install	Install packages.
download	Download packages.
uninstall	Uninstall packages.
freeze	Output installed packages in requirements format.
inspect	Inspect the python environment.
list	List installed packages.
show	Show information about installed packages.
check	Verify installed packages have compatible dependencies.
config	Manage local and global configuration.
search	Search PyPI for packages.
cache	Inspect and manage pip's wheel cache.
index	Inspect information available from package indexes.
wheel	Build wheels from your requirements.
hash	Compute hashes of package archives.
completion	A helper command used for command completion.
debug	Show info useful for debugging.

system

import sys
sys.path

where python && which python

Print

print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

Prints the values to a stream, or to sys.stdout by default
Optional keyword arguments:
- file: a file-like object (stream); defaults to the current sys.stdout.
- sep: string inserted between values, default a space.
- end: string appended after the last value, default a newline
- flush: whether to forcibly flush the stream.

Class

int([x]) -> integer int(x, base=10) -> integer
# Convert a number or string to an integer

Sequence types: strings, lists, tuples, bytes sequences, bytes arrays, range() objects

Strings

'str'.join

Concatenate any number of strings.

The string whose method is called is inserted in between each given string. The result is returned as a new string.

Example: '.'.join(['ab', 'pq', 'rs']) -> 'ab.pq.rs'

'str'.format() S.format(*args, **kwargs) -> str Return a formatted version of S, using substitutions from args and kwargs. The substitutions are identified by braces ('{' and '}').
'str'.split() S.format(*args, **kwargs) -> str Return a formatted version of S, using substitutions from args and kwargs. The substitutions are identified by braces ('{' and '}').
'str'.lstrip() Return a copy of the string with leading whitespace removed.
'str'.upper() | 'str'.capatilize() to cap only first letter in str Return a copy of the string converted to uppercase.
'str'.isupper, isalphanum, isnumeric, isalpha, isdigit etc.
- returns True or False
Use double quotes, or an escape char ()
- Everything inside the double quote will be printed to stdout
\n for new line
- use print() func for \n to work
raw string: add r before the first quote so chars prefaced by \ aren't viewed as special chars
triple quotes allow string literals to span multiple lines
- use \ to prevent the end of line at start
in indexing and slicing
- start is always included, and the end always excluded.
- an omitted first index defaults to zero, an omitted second index defaults to size of the string being sliced

'hasn\'t'
"hasn't"
print('''\
    Topic: Python
    Date: Oct. 06
''')
print(r'C:\some\name')

File Handling

"r" Read - default value; Opens a file for reading, error if file !exist
"a" Append - opens for appending; creates if !exist
- open for writing, appending to the end of the file if it exists
"w" write - opens a file for writing and creates if it doesn't exit
- truncating the file first
"x" Create - creates specified file; error if file == exist
- can specify if file should be handled as binary(ex. images) or text mode
'b' binary mode
't' text mode (default)
'+' open a disk file for updating (reading and writing)

f = open("demo.txt")
print(f.read())

def ex_pr(file):
  return print(f.readline('file'))

fa = open("D:/Docs/welcome.txt", "r")
print(f.read(5))
# open and read file => view first 5 chars

fa.close()

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PyDoc.md

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Python Base Info

Terms

To-Do

Argument passing

virtual env creation

Pip commands

system

Print

Class

Sequence types: strings, lists, tuples, bytes sequences, bytes arrays, range() objects

Strings

File Handling

API Info

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Python Base Info

Terms

To-Do

Argument passing

virtual env creation

Pip commands

system

Print

Class

Sequence types: strings, lists, tuples, bytes sequences, bytes arrays, range() objects

Strings

File Handling

API Info