← QCE Digital Solutions Unit 2

Streams of structured data

A sequence of structured records that arrives or is read one at a time, such as sensor readings, file lines or API results, and is processed as it flows.

Part of: QCE Digital Solutions Unit 2 — Data and Programming Techniques — Module 51

Understanding Streams of structured data in QCE Digital Solutions Unit 2

What it does: The loop body runs once per record. This shows the one-record-at-a-time idea of a stream. Each API result is a structured record. Looping over them handles them one by one, like any other stream. Sensor readings are a classic stream: each reading arrives in order and can be processed as it comes in. API results can be read record by record. A single variable holds one value, not a sequence of records. Processing as the data flows is the key idea of a stream. Structured records share the same fields, so the program knows where to find each value. Because records flow one at a time, processing can begin straight away.

Common mistakes: A for loop header must end with a colon. It should be: for line in file:. range() needs a number, not a list. To read each sensor reading one at a time, loop directly: for r in readings:.

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This module's key terms are also in a printable crossword (Modules 186–228) and word search (Modules 144–228).

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Learning

Duo

Which best describes a stream of records?

Records that arrive or are read one at a time and processed as they flowAll records loaded into memory at once before any processing starts

Matches

data = open("readings.csv").read() for line in data:

↓

read() loads the whole file into one string, so the loop gets single characters instead of lines. It no longer treats the file as a stream of records.

Applying

Meanings

Term

stream

Meaning

A sequence of structured records that arrives or is read one at a time, such as sensor readings, file lines or API results, and is processed as it flows.

Practice

readings = ["Mon,24", "Tue,27", "Wed,31"]

Testing

Gaps

reading in sensorstream:

Check Answer

Spots

1file = open("temps.csv")

2for line in file

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Quick Questions

1. Which best describes a stream of records?

A. Records that arrive or are read one at a time and processed as they flow ✓

B. All records loaded into memory at once before any processing starts

A stream is handled one record at a time, so you do not need the whole dataset stored first.

2. A temperature sensor sends a new reading every second. Is this a stream?

A. Yes, each reading arrives one at a time as a structured record ✓

B. No, sensor readings can only be processed after the sensor stops

Sensor readings are a classic stream: each reading arrives in order and can be processed as it comes in.

3. A program reads a CSV file by looping over its lines. Each line is treated as:

A. One record in the stream ✓

B. The entire stream at once

Each line in a file is one record. The loop reads them one at a time, so the file acts as the stream.

4. Which is an example of a stream source?

A. A single integer variable called total

B. Results returned by an API, read one record at a time ✓

API results can be read record by record. A single variable holds one value, not a sequence of records.

5. In a stream, when is each record processed?

A. Only after every record has been collected into one big array

B. As it is read, one record at a time ✓

Processing as the data flows is the key idea of a stream.

Match the Pairs

for line in open("readings.csv"): → Reads a file as a stream, giving the program one line (one record) at a time

for reading in sensor_feed: → Processes sensor readings one record at a time as they arrive

A stream is processed one record at a time, so a loop handles each record in turn → for record in stream: print(record)

API results can be treated as a stream of records, with each result processed as it is read → for result in api_results: process(result)

data = open("readings.csv").read() for line in data: → read() loads the whole file into one string, so the loop gets single characters instead of lines. It no longer treats the file as a stream of records.

for reading in sensor_feed: total = reading print(total) → The loop replaces total with each reading instead of adding to it, so nothing builds up as the stream flows. The code should use total = total + reading, after setting total to 0 before the loop.

Key Term

stream

A sequence of structured records that arrives or is read one at a time, such as sensor readings, file lines or API results, and is processed as it flows.

Fill in the Blanks

1. for reading in sensor_stream: print(reading)

Hint: Type the keyword that repeats the loop body once for each item in the stream.

2. for line in open("log.csv"): print(line)

Hint: Type the function that opens a file so its lines can be read one at a time.

3. for record in api_results: print(record)

Hint: Type the keyword that connects the loop variable to the stream of API results it takes records from.

4. total = 0 for r in readings: total = total + r["temp"]

Hint: Type the arithmetic operator that adds each reading's value to the running total.

5. for line in open("data.csv"): fields = line.split(",") print(fields[0])

Hint: Type the string method that breaks one line of the stream into a list of fields.

Spot the Error

Question 1

A file = open("temps.csv")

B for line in file

C parts = line.split(",")

D print(parts[0])

Line B — A for loop header must end with a colon. It should be: for line in file:

Question 2

A total = 0

B for r in range(readings):

C total = total + r

D print(total)

Line B — range() needs a number, not a list. To read each sensor reading one at a time, loop directly: for r in readings:

Question 3

A for line in open("log.csv"):

B fields = line.split(",")

C temp = float(fields(1))

D print(temp)

Line C — A list item is picked with square brackets, not round ones. It should be: temp = float(fields[1])

Question 4

A with open(data.csv) as f:

B for line in f:

C print(line.strip())

Line A — The file name is text, so it needs quotes. Without them Python looks for variables called data and csv. It should be: with open("data.csv") as f:

Question 5

A results = get_results(url)

B for item in results:

C name = item["name"]

D print(Name)

Line D — Variable names are case sensitive. The variable was created as name, so Name does not exist. It should be: print(name)

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