Merge pull request #435 from realpython/python-f-string

Sample code for the article on f-strings

python-f-string/README.md

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+# Python's F-String: An Improved String Interpolation and Formatting Tool
+
+This folder provides the code examples for the Real Python tutorial [Python's F-String: An Improved String Interpolation and Formatting Tool](https://realpython.com/python-f-string-update/).

python-f-string/basic_f_strings.py

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+name = "Jane"
+age = 25
+
+print(f"Hello, {name}! You're {age} years old.")
+
+print(f"{2 * 21}")

python-f-string/basic_format_method.py

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+name = "Jane"
+age = 25
+
+print("Hello, {}! You're {} years old.".format(name, age))
+print("Hello, {name}! You're {age} years old.".format(name="Jane", age=25))

python-f-string/basic_modulo.py

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+name = "Jane"
+age = 25
+
+print("Hello, %s!" % name)
+print("Hello, %s! You're %s years old." % (name, age))

python-f-string/dictionaries.py

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+person = {"name": "Jane Doe", "age": 25}
+
+print(f"Hello, {person['name']}! You're {person['age']} years old.")
+
+print("Hello, {name}! You're {age} years old.".format(**person))
+print("Hello, {name}!".format(**person))
+
+print("Hello, %(name)s! You're %(age)s years old." % person)
+print("Hello, %(name)s!" % person)

python-f-string/f_strings_doc_expressions.py

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+variable = "Some mysterious value"
+
+print(f"{variable = }")

python-f-string/f_strings_expressions.py

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+name = "Jane"
+age = 25
+
+print(f"Hello, {name.upper()}! You're {age} years old.")
+print(f"{[2**n for n in range(3, 9)]}")

python-f-string/f_strings_representation.py

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+from person import Person
+
+jane = Person("Jane Doe", 25)
+
+print(f"{jane!s}")
+print(f"{jane!r}")

python-f-string/format_f_string.py

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+balance = 5425.9292
+print(f"Balance: ${balance:.2f}")
+
+heading = "Centered string"
+print(f"{heading:=^30}")
+
+integer = -1234567
+print(f"Comma as thousand separators: {integer:,}")
+sep = "_"
+print(f"User's thousand separators: {integer:{sep}}")
+
+floating_point = 1234567.9876
+print(f"Comma as thousand separators and two decimals: {floating_point:,.2f}")
+
+date = (9, 6, 2023)
+print(f"Date: {date[0]:02}-{date[1]:02}-{date[2]}")
+date = (9, 26, 2023)
+print(f"Date: {date[0]:02}/{date[1]:02}/{date[2]}")

python-f-string/format_format_method.py

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+print("Balance: ${:.2f}".format(5425.9292))
+
+print("{:=^30}".format("Centered string"))

python-f-string/format_modulo.py

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+print("Balance: $%.2f" % 5425.9292)
+
+print("Name: %s\nAge: %5s" % ("John", 35))

python-f-string/i18n_format_method.py

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+greeting_template = "{greeting} Pythonista!"
+
+greeting_en = "Good Morning!"
+greeting_es = "¡Buenos días!"
+greeting_fr = "Bonjour!"
+
+for greeting in (greeting_en, greeting_es, greeting_fr):
+    print(greeting_template.format(greeting=greeting))

python-f-string/logging_modulo.py

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+import logging
+
+msg = "This is a %s message!"
+
+logging.warning(msg, "WARNING")
+
+logging.debug(msg, "DEBUGGING")

python-f-string/performance.py

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+import timeit
+
+name = "Linda Smith"
+age = 40
+strings = {
+    "Modulo operator": "'Name: %s Age: %s' % (name, age)",
+    ".format() method": "'Name: {} Age: {}'.format(name, age)",
+    "f_string": "f'Name: {name} Age: {age}'",
+}
+
+
+def run_performance_test(strings):
+    max_length = len(max(strings, key=len))
+    for tool, string in strings.items():
+        time = timeit.timeit(string, number=1000000, globals=globals()) * 1000
+        print(f"{tool}: {time:>{max_length - len(tool) + 6}.2f} ms")
+
+
+run_performance_test(strings)

python-f-string/person.py

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+class Person:
+    def __init__(self, name, age):
+        self.name = name
+        self.age = age
+
+    def __str__(self):
+        return f"I'm {self.name}, and I'm {self.age} years old."
+
+    def __repr__(self):
+        return f"{type(self).__name__}(name='{self.name}', age={self.age})"

python-f-string/sample_v1.py

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+name = "Jane"
+age = 25
+
+print("Hello, %s! You're %s years old." % (name, age))

python-f-string/sample_v2.py

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+name = "Jane"
+age = 25
+
+print(f"Hello, {name}! You're {age} years old.")

python-f-string/sql_queries.py

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+import psycopg2
+
+# This code doesn't run because of the missing `psycopg2` library
+# and the assumption of a certain database structure and setup.
+# It's a demonstrative code only.
+
+connection = psycopg2.connect(database="db", user="user", password="password")
+cursor = connection.cursor()
+
+role = "admin"
+
+query_modulo = "SELECT * FROM users WHERE role = '%s'" % role
+query_format = "SELECT * FROM users WHERE role = '{role}'".format(role=role)
+query_f_string = f"SELECT * FROM users WHERE role = '{role}'"
+
+cursor.execute(query_modulo)
+cursor.execute(query_format)
+cursor.execute(query_f_string)
+
+# Correct query
+query_template = "SELECT * FROM users WHERE role = %s"
+
+cursor.execute(query_template, (role,))