Merge branch 'master' into pandas-gradebook

Author: jaschmitt

python-import/README.md

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+# Python `import`: Advanced Techniques and Tips
+
+This folder contains code and materials used in Real Python's [Python `import`: Advanced Techniques and Tips]() article.
+

python-import/cyclical_imports/yang.py

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+# yang.py
+
+print("Hello from yang")
+import yin  # noqa
+
+number = 24
+
+
+def combine():
+    return number + yin.number
+
+
+print(f"yin and yang combined is {combine()}")
+print("Goodbye from yang")

python-import/cyclical_imports/yin.py

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+# yin.py
+
+print("Hello from yin")
+number = 42
+
+
+def combine():
+    import yang
+
+    return number + yang.number
+
+
+print("Goodbye from yin")

python-import/docreader.py

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+# docreader.py
+
+import importlib
+
+module_name = input("Name of module? ")
+module = importlib.import_module(module_name)
+print(module.__doc__)

python-import/feel_young.py

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+# feel_young.py
+
+
+def make_young(text):
+    words = [replace_by_age(w) for w in text.split()]
+    return " ".join(words)
+
+
+def replace_by_age(word, new_age=24, age_range=(25, 120)):
+    if word.isdigit() and int(word) in range(*age_range):
+        return str(new_age)
+    return word
+
+
+if __name__ == "__main__":
+    text = input("Tell me something: ")
+    print(make_young(text))

python-import/finders_and_loaders/ban_importer.py

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+# ban_importer.py
+
+import sys
+
+BANNED_MODULES = {"re"}
+
+
+class BanFinder:
+    @classmethod
+    def find_spec(cls, name, path, target=None):
+        if name in BANNED_MODULES:
+            raise ModuleNotFoundError(f"{name!r} is banned")
+
+
+sys.meta_path.insert(0, BanFinder)

python-import/finders_and_loaders/csv_importer.py

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+# csv_importer.py
+
+import csv
+import pathlib
+import re
+import sys
+from importlib.machinery import ModuleSpec
+
+
+class CsvImporter:
+    def __init__(self, csv_path):
+        """Store path to CSV file"""
+        self.csv_path = csv_path
+
+    @classmethod
+    def find_spec(cls, name, path, target=None):
+        """Look for CSV file"""
+        package, _, module_name = name.rpartition(".")
+        csv_file_name = f"{module_name}.csv"
+        directories = sys.path if path is None else path
+        for directory in directories:
+            csv_path = pathlib.Path(directory) / csv_file_name
+            if csv_path.exists():
+                return ModuleSpec(name, cls(csv_path))
+
+    def create_module(self, spec):
+        """Returning None uses the standard machinery for creating modules"""
+        return None
+
+    def exec_module(self, module):
+        """Executing the module means reading the CSV file"""
+        # Read CSV data and store as a list of rows
+        with self.csv_path.open() as fid:
+            rows = csv.DictReader(fid)
+            data = list(rows)
+            fieldnames = tuple(_identifier(f) for f in rows.fieldnames)
+
+        # Create a dict with each field
+        values = zip(*(row.values() for row in data))
+        fields = dict(zip(fieldnames, values))
+
+        # Add the data to the module
+        module.__dict__.update(fields)
+        module.__dict__["data"] = data
+        module.__dict__["fieldnames"] = fieldnames
+        module.__file__ = str(self.csv_path)
+
+    def __repr__(self):
+        """Nice representation of the class"""
+        return f"{self.__class__.__name__}({str(self.csv_path)!r})"
+
+
+def _identifier(var_str):
+    """Create a valid identifier from a string
+
+    See https://stackoverflow.com/a/3305731
+    """
+    return re.sub(r"\W|^(?=\d)", "_", var_str)
+
+
+# Add the CSV importer at the end of the list of finders
+sys.meta_path.append(CsvImporter)

python-import/finders_and_loaders/debug_importer.py

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+# debug_importer.py
+
+import sys
+
+
+class DebugFinder:
+    @classmethod
+    def find_spec(cls, name, path, target=None):
+        print(f"Importing {name!r}")
+        return None
+
+
+sys.meta_path.insert(0, DebugFinder)

python-import/finders_and_loaders/employees.csv

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+name,department,birthday month
+John Smith,Accounting,November
+Erica Meyers,IT,March

python-import/finders_and_loaders/pip_importer.py

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+# pip_importer.py
+
+from importlib import util
+import subprocess
+import sys
+
+
+class PipFinder:
+    @classmethod
+    def find_spec(cls, name, path, target=None):
+        print(f"Module {name!r} not installed.  Attempting to pip install")
+        cmd = f"{sys.executable} -m pip install {name}"
+        try:
+            subprocess.run(cmd.split(), check=True)
+        except subprocess.CalledProcessError:
+            return None
+
+        return util.find_spec(name)
+
+
+sys.meta_path.append(PipFinder)