Strings and text

Creating and combining strings

Use single or double quotes. For multi-line text (prompts, docs) use triple quotes """...""".

Concatenate with +, or better, f-strings: f"Model {name} scored {score:.2f}". F-strings keep prompts readable.

len(s) is the number of characters, not tokens. Character length is still a useful proxy when you do not have a tokenizer loaded.

Strings are immutable. s.upper() returns a new string; s does not change unless you assign the result back.

Slicing, splitting, and stripping

Indexing: s[0] is the first character. s[-1] is the last. Slices: s[0:50] is the first 50 characters (end index is exclusive).

split() breaks on whitespace by default — useful for a crude word count. strip() removes leading/trailing whitespace, which you should do on every user prompt before sending it to a model.

in checks substring membership: "error" in message.lower().

Escape sequences: \n is a newline. In prompts, extra blank lines change model behaviour more than people expect — keep prompt templates tidy.

Copy-paste examples

Copy into your own editor, or load one into the compiler below and press Run.

user_question = "What is MLOps?"
context = "MLOps is how teams deploy and monitor ML models."

prompt = f"""You are a precise assistant.
Use only the context.

Context:
{context}

Question: {user_question}
Answer:"""

print(prompt)
print("---")
print("characters:", len(prompt))

raw = "   What is RAG?   \n"
clean = raw.strip()
print(repr(raw))
print(repr(clean))
print("empty?", clean == "")
print("too long?", len(clean) > 4000)
print("words (rough):", len(clean.split()))

doc = "Retrieval-Augmented Generation grounds an LLM in your own documents."
preview = doc[:40]
print(preview + ("..." if len(doc) > 40 else ""))
print("starts with Retrieval?", doc.startswith("Retrieval"))
print("mentions LLM?", "LLM" in doc)

Takeaways

• f-strings are the clean way to build prompts and log lines.
• strip() user text; len() is characters, not tokens.
• Strings never change in place — methods return new strings.