A basic example of reading and writing CSV files/data

Python/045_filedata.py

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+# File Data Input/Output
+
+import os
+from dataclasses import dataclass
+from pathlib import Path
+
+# We will start combining much of what we've learned so far
+# as we begin talking about more complex subjects. The first
+# example will be working with a CSV (Comma Separated Value)
+# file used to store user data.
+
+# We create a data class named User()
+@dataclass
+class User():
+    email: str = ""
+    id: int = 0
+    first_name: str = ""
+    last_name: str = ""
+
+# Build up the path to the data file
+data_file = os.path.join("Data", "users.csv")
+# The pathlib module provides streamlined methods of getting
+# the entire contents of a file in one command.
+# This is a fairly complex statement.
+#    1) Create a Path() object to the data_file
+#    2) Use the read_text() method to read in the entire file as a string
+#    3) Use the split() method on the string data to split it into lines
+#    4) Use a slice ([1:]) to remove the first line (the header)
+csv_contents = Path(data_file).read_text().split("\n")[1:]
+# The list which will contain User() objects
+users = []
+# Step through the lines one at a time
+for line in csv_contents:
+    # Split the line on commas after stripping leading/trailing white space
+    parts = line.strip().split(",")
+    # If we don't get four elements from the split then go to the next line
+    if len(parts) != 4:
+        continue
+    # Create a new User() object from the split parts of the line
+    users.append(User(parts[0], parts[1], parts[2], parts[3]))
+
+# Print them out
+for user in users:
+    print(user)
+
+# Now we'll write the data we have back to a new file.
+# In this repository any file beginning with "test_" will
+# be ignored so we'll use a file names of "test_userdata.csv"
+
+csv_filename = os.path.join("Data", "test_userdata.csv")
+# We open the file. If the open fails it just quietly continues
+with open(csv_filename, "w") as f:
+    # Let's write a header to the CSV
+    line = "EMail Address,User ID,First Name,Last Name\n"
+    f.write(line)
+    # Now we walk through the user data and write it all to the file
+    user: User
+    for user in users:
+        line = user.email + ","
+        line += user.id + ","
+        line += user.first_name + ","
+        line += user.last_name + "\n"
+        f.write(line)
+    print(f"User data written to file: {csv_filename}")

Python/Data/users.csv

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+Login email,Identifier,First name,Last name
+laura@example.com,2070,Laura,Grey
+craig@example.com,4081,Craig,Johnson
+mary@example.com,9346,Mary,Jenkins
+jamie@example.com,5079,Jamie,Smith