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Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/alembic.ini

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+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = alembic
+
+# template used to generate migration files
+# file_template = %%(rev)s_%%(slug)s
+
+# timezone to use when rendering the date
+# within the migration file as well as the filename.
+# string value is passed to dateutil.tz.gettz()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the
+# "slug" field
+#truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; this defaults
+# to alembic/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path
+# version_locations = %(here)s/bar %(here)s/bat alembic/versions
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+sqlalchemy.url = driver://user:pass@localhost/dbname
+
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/alembic/README

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+Generic single-database configuration.

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/alembic/env.py

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+from __future__ import with_statement
+from alembic import context
+from sqlalchemy import engine_from_config, pool
+from logging.config import fileConfig
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+fileConfig(config.config_file_name)
+
+import sys, os
+sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
+
+import config as my_config
+config.set_main_option('sqlalchemy.url', my_config.DATABASE_URI)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+from models import Base
+target_metadata = Base.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline():
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url, target_metadata=target_metadata, literal_binds=True)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online():
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section),
+        prefix='sqlalchemy.',
+        poolclass=pool.NullPool)
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection,
+            target_metadata=target_metadata
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/alembic/script.py.mako

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+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade():
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade():
+    ${downgrades if downgrades else "pass"}

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/alembic/versions/c98ef4af563a_added_price_column.py

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+"""Added price column
+
+Revision ID: c98ef4af563a
+Revises: 
+Create Date: 2018-12-31 13:03:51.242265
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = 'c98ef4af563a'
+down_revision = None
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('books', sa.Column('price', postgresql.MONEY(), nullable=True))
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('books', 'price')
+    # ### end Alembic commands ###

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/books.yaml

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+title: "An Introduction to Statistical Learning: with Applications in R"
+author: Gareth James, Daniela Witten, Trevor Hastie, and Robert Tibshirani
+pages: 426
+published: 01-01-2013
+---
+title: "The Elements of Statistical Learning: Data Mining, Inference and Prediction"
+author: Trevor Hastie, Robert Tibshirani, Jerome Friedman
+pages: 745
+published: 01-01-2009
+---
+title: "Pattern Recognition and Machine Learning"
+author: Christopher Bishop
+pages: 738
+published: 04-06-2011
+---
+title: "Machine Learning: A Probabilistic Perspective"
+author: Kevin Murphy
+pages: 1104
+published: 08-24-2012
+---
+title: "Deep Learning"
+author: Ian Goodfellow, Yoshua Bengio, Aaron Courville, Francis Bach
+pages: 775
+published: 10-08-2016

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/cli.py

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+from crud import Session
+from models import Book
+
+s = Session()
+
+books = s.query(Book).all()
+
+for book in books:
+    price = input(f"Price for '{book.title}': $")
+    book.price = price
+    s.add(book)
+
+s.commit()
+s.close()

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/config.py

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+
+DATABASE_URI = 'postgres+psycopg2://postgres:password@localhost:5432/books'

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/crud.py

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+from datetime import datetime
+
+from sqlalchemy import create_engine
+from config import DATABASE_URI
+from models import Base, Book
+from sqlalchemy.orm import sessionmaker
+from contextlib import contextmanager
+import yaml
+
+engine = create_engine(DATABASE_URI)
+
+Session = sessionmaker(bind=engine)
+
+
+@contextmanager
+def session_scope():
+    session = Session()
+    try:
+        yield session
+        session.commit()
+    except Exception:
+        session.rollback()
+        raise
+    finally:
+        session.close()
+
+
+def recreate_database():
+    Base.metadata.drop_all(engine)
+    Base.metadata.create_all(engine)
+
+
+def load_yaml():
+    with session_scope() as s:
+        for data in yaml.load_all(open('books.yaml')):
+            book = Book(**data)
+            s.add(book)
+
+
+if __name__ == '__main__':
+    recreate_database()
+    # add_data()
+
+    book = Book(
+            title='Deep Learning',
+            author='Ian Goodfellow',
+            pages=775,
+            published=datetime(2016, 11, 18)
+    )
+    with session_scope() as s:
+        s.add(book)

Guide to Using Databases with Python Postgres, SQLAlchemy, and Alembic/project/models.py

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+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy import Column, Integer, String, Date
+from sqlalchemy.dialects.postgresql import MONEY
+
+Base = declarative_base()
+
+class Book(Base):
+    __tablename__ = 'books'
+    id = Column(Integer, primary_key=True)
+    title = Column(String)
+    author = Column(String)
+    pages = Column(Integer)
+    published = Column(Date)
+    price = Column(MONEY)
+
+    def __repr__(self):
+        return "<Book(title='{}', author='{}', pages={}, published={}, price={})>" \
+            .format(self.title, self.author, self.pages, self.published, self.price)