R and Python Together: A Second Case Study Using LangChain’s LLM Tools

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Following my previous post, I am again looking at how to employ R and Python seamlessly to use large language models (LLMs). Last time, I scraped information off of Wikipedia using the rvest package, fed that information to OpenAI’s Python API, and asked it to extract information for me.

But what if we could skip that scraping step? What if we had a more complex question where writing an rvest or RSelenium script was not feasible?

Enter the LangChain Python library. I recently read Generative AI with LangChain and Developing Apps with GPT-4 and ChatGPT, both of which do a fabulous job of introducing LangChain’s capabilities.

I’ve been thinking of LangChain as an LLM version of scikit-learn: It is a model-agnostic framework where you can build LLM pipelines. Most relevant to our needs here, though, is that you can employ tools in these pipelines. Tools allow the LLM to rely on integrations to answer prompts. One tool is Wikipedia, which allows the LLM to search and read Wikipedia in trying to answer the question it’s been given. This is especially useful if you want to ask it information about something that happened after it was trained.

I’m continuing to use my Best Picture model as the project, using LLMs to get more features for me to add to it. This means I’m mostly using LLMs as information extractors instead of information generators. Does this really map one-to-one with what something like GPT 3.5 Turbo was meant to do? I truly don’t know. I don’t think many people know what the hell these things can and should be used for. Which is why I’m testing it and reporting out the accuracy here!


Past Lives (my favorite movie of last year) was nominated for Best Picture, even though it was director Celine Song’s debut feature-length film. This is rare, and I think a helpful feature for my Best Picture model would be how many films the director had directed before the nominated film.

Getting this information is a bit more complicated. It would involve an RSelenium script of going to the movie’s page, finding the director, clicking on their profile, and then either pulling down filmography information from there or by clicking into their filmography page. Pages aren’t formatted the same, either. Sometimes the section is “Filmography,” sometimes it is “Works,” sometimes the information is in a table, while other times it is in a bulleted list.

The idea here is to use LangChain to give an LLM the Wikipedia tool to find this information for me. As opposed to my last post, I am not giving it the relevant slice of info from Wikipedia anymore. Instead, I asking it a question and giving it Wikipedia as a tool to use itself.


I took the following steps:

  1. Wrote a prompt that asks an LLM to figure out how many feature-length films the director of a movie had directed before making a film. The prompt is a template that takes a film’s name and release year.

  2. Give the LLM the Wikipedia tool and a calculator (my thinking was it might need this to sum up the number of movies, since these models are optimized on language, not math).

  3. Collect and clean the responses for every movie that’s been nominated for Best Picture.

  4. Test the accuracy by hand-checking 100 of these cases.

The Prompt and Function

I started by making a file named funs.py:

from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain.agents import load_tools, AgentExecutor, create_openai_tools_agent
from re import sub

model = ChatOpenAI(
tools = load_tools(["wikipedia", "llm-math"], llm=model)
prompt = ChatPromptTemplate.from_messages(
    ("system", """You are a helpful research assistant, and your job is to
                  retrieve information about movies and movie directors. Think
                  through the questions you are asked step-by-step."""),
    ("human", """How many feature films did the director of the  movie 
                  direct before they made ? First, find who
                 directed . Then, look at their filmography. Find all the
                 feature-length movies they directed before . Only 
                 consider movies that were released. Lastly, count up how many 
                 movies this is. Think step-by-step and write them down. When 
                 you have an answer, say, 'The number is: ' and give the
agent = create_openai_tools_agent(model, tools, prompt)
agent_executor = AgentExecutor(agent=agent, tools=tools, max_iterations=6)

def prior_films(year, film):
  resp = agent_executor.invoke({"year": year, "name": film})

It turns out that many of the functions in the two books above, despite being Published in October and December of 2023, have been deprecated (but the author of Developing Apps has published updated code and a second version of the book is being released this year). This is a good reminder of how quickly this field is moving, and it’s OK to not be entirely sure how to use these models—so long as you have appropriate respect for that lack of knowledge. This is to say: I’m no expert here. What I have above is cobbled together from LangChain docs, StackOverflow posts, and GitHub threads. The prompt here lays out the basic steps it should be following to get the information.

Bringing It To R

I wrote an R script to use this function in an R session. Why? Because I think the tidyverse makes it easier to inspect, clean, and wrangle data than anything in Python currently.

We start off by loading the R packages, sourcing the R script, activating the Python virtual environment (the path is relative to my file structure in my drive), and sourcing the Python script. I read in the data from a Google Sheet of mine and do one step of cleaning, as the read_sheet() function was bringing the title variable in as a list of lists instead of a character vector. I then initialize a new column, resp, where I will collect the responses from the LLM.


dat <- read_sheet("17--EbmRR9cSZCNgI_pFAFPsdCR5DLoYmnoofWRSdxkI") %>%
  mutate(film = as.character(film)) %>%
  select(year, film) %>%
  mutate(resp = NA)

I iterate through each film using a for loop. This is not the R way, I know, but if something snags, I want to catch the response that I’m paying for. You’ll see that I take extra precautions to catch everything by writing out the results in .csv row-by-row. (My solution because I had been running this script and got an aborted R session in the middle and lost everything.)

for (r in 1:nrow(dat)) {
  cat("prompting", r, "\n")
  dat$resp[r] <- str_replace_all(
    prior_films(dat$year[r], dat$film[r]),
    " "

  cat("writing", r, "\n")
  if (r == 1) {
    write_csv(dat[r, ], "prior_films.csv")
  } else {
    write_csv(dat[r, ], "prior_films.csv", append = TRUE)

  Sys.sleep(runif(1, 2, 10))

As I said in my previous post, this is an example of how we can use R and Python together in harmony. prior_films is a Python function, but we use it inside of an R script.

An example call that returns the correct information:

> prior_films(2017, "phantom thread")
[1] "The director of the movie \"Phantom Thread\" is Paul Thomas Anderson. Before directing \"Phantom Thread\" in 2017, Paul Thomas Anderson directed the following feature-length movies that were released:\n\n1. Hard Eight (1996)\n2. Boogie Nights (1997)\n3. Magnolia (1999)\n4. Punch-Drunk Love (2002)\n5. There Will Be Blood (2007)\n6. The Master (2012)\n7. Inherent Vice (2014)\n\nThe number of feature films that Paul Thomas Anderson directed before making \"Phantom Thread\" in 2017 is 7."

I then pulled in this .csv to a separate cleaning script. Since I asked it for standardized feedback, I could use a regular expression to clean most of the responses. I read the rest myself. This went into a new column called resp_clean, with only the integer representing the number of movies the director had directed before the movie in question.


dat <- read_csv("prior_films.csv")

dat <- dat %>% 
    resp_clean = case_when(
      str_detect(tolower(resp), "the number(.*)is") ~ 
        str_split_i(tolower(resp), "the number(.*)is", 2)
    resp_clean = str_remove_all(resp_clean, "[^0-9]")

# manual code the rest
lgl <- !is.na(dat$resp) & 
  dat$resp != "Agent stopped due to max iterations." &

dat$resp[lgl] # read with mine own human eyes
dat$resp_clean[lgl] <- c(NA, NA, 44, NA, NA,
                         NA, NA, NA, NA, NA,
                         4,  NA, NA, 86, NA,
                         9,  NA,  4, 33, 26)


I used OpenAI’s GPT 3.5 Turbo alone this time. The trade-off of using the Wikipedia tool in LangChain is there are many, many more “context tokens,” which can drive up the expense of each prompt quite a bit (hence no GPT 4). I also set the temperature to zero to get a more reproducible and the most probable response each time. You could set this higher to get more “creative” responses, but that is not what I want from information extraction.

I was able to get valid responses for 81% of the films, which meant the LLM couldn’t find an answer for 115 of them. It either told me it couldn’t find the information or simply said "Agent stopped due to max iterations.", which meant it couldn’t find the answer in the limited six steps I gave it (so as to not run up a bill by the model running in circles, reading the same few Wikipedia pages over and over).


First, let’s look at the correlation between GPT 3.5 Turbo’s responses and the hand-checked responses, alongside a scatterplot. The purple line is a smoothed loess, while the green line is OLS. The dotted black line would be perfect performance, where hand-checked equals GPT 3.5 Turbo. This also means any dot above the line is an undercount, while any below it is an overcount.


dat <- read_csv("performance.csv")

cor.test( ~ check + resp_clean, dat)
##  Pearson's product-moment correlation
## data:  check and resp_clean
## t = 3.8741, df = 98, p-value = 0.0001934
## alternative hypothesis: true correlation is not equal to 0
## 95 percent confidence interval:
##  0.1809637 0.5233826
## sample estimates:
##       cor 
## 0.3644284
ggplot(dat, aes(x = resp_clean, y = check)) +
  geom_abline(aes(intercept = 0, slope = 1), linetype = "dotted") +
  geom_point(alpha = .5) +
  geom_smooth(method = "loess", se = FALSE, span = .95, color = "purple") +
  geom_smooth(method = "lm", se = FALSE, color = "forestgreen") +
  theme_light() +
  labs(x = "Hand-Checked", y = "GPT 3.5 Turbo")

Oof, some huge misses. Not great performance from the LLM here. Most of these huge misses are due to early filmmakers and the studio system, which would churn out massive amounts of films, especially during the silent era. So, let’s look at absolute error by year.

Error by Year

dat <- dat %>% 
  mutate(abs_err = abs(resp_clean - check))
dat %>% 
  summarise(mae = mean(abs_err))
## # A tibble: 1 × 1
##     mae
##   <dbl>
## 1   9.7
dat %>%
  mutate(err_disc = case_when(
    (check - resp_clean) > 0 ~ "Undercount",
    (check - resp_clean) < 0 ~ "Overcount",
    (check - resp_clean) == 0 ~ "Correct"
  )) %>%
## # A tibble: 3 × 2
##   err_disc       n
##   <chr>      <int>
## 1 Correct       28
## 2 Overcount     15
## 3 Undercount    57

We get a mean absolute error of nearly ten films. We also see that the model gave us the correct answer 28% of the time, an undercount 57%, and an overcount 15%.

When we plot absolute error against release year, we can see the poor performance is driven by earlier films:

ggplot(dat, aes(x = year, y = abs_err)) +
  geom_abline(aes(intercept = 0, slope = 1), linetype = "dotted") +
  geom_point(alpha = .5) +
  geom_smooth(method = "loess", se = FALSE, span = .95, color = "purple") +
  geom_smooth(method = "lm", se = FALSE, color = "forestgreen") +
  theme_light() +
  labs(x = "Year", y = "Absolute Error")

So how about we remove the studio-era films, since that wouldn’t be a good input into a model trying to predict Best Picture next year anyways? The cleanest cutoff I could think of is 1970 and later, since RKO closed in 1969:

dat %>% 
  filter(year > 1969) %>% # year RKO closed
  summarise(mae = mean(abs_err))
## # A tibble: 1 × 1
##     mae
##   <dbl>
## 1  1.52

We’re still off by 1.5 films, which is still more error than I’d like to include in my model. (Spoiler: I won’t be using the data generated here for my Best Picture model.)

Problematic Films and Directors

Let’s look at which films were the biggest misses, with an error of more than thirty films.

ggplot(dat, aes(x = resp_clean, y = check)) +
  geom_abline(aes(intercept = 0, slope = 1), linetype = "dotted") +
  geom_point(alpha = .5) +
  geom_smooth(method = "loess", se = FALSE, span = .95, color = "purple") +
  geom_smooth(method = "lm", se = FALSE, color = "forestgreen") +
  theme_light() +
  labs(x = "Hand-Checked", y = "GPT 3.5 Turbo") +
  ggrepel::geom_text_repel(aes(label = ifelse(abs_err > 30, film, "")))

The directors in question here are W.S. Van Dyke, Michael Curtiz, John Ford, William Wyler, and Edmund Goulding. I would invite you to visit their Wikipedia pages and try to make sense of their filmography sections; it’s a lot. John Ford’s page, for example, lists all of the informational “short films” he made with the military, including Sex Hygiene and How to Operate Behind Enemy Lines. These pages were hard for me to hand-code according to the prompt.


Lastly, let’s examine overcounts. It makes more intuitive sense to get an undercount: The model didn’t pick up on films the person already directed—it missed them. But an overcount is stranger: How does that happen? A few examples:

> prior_films(2009, "district 9")
[1] "The feature-length movies directed by Neill Blomkamp before he made \"District 9\" in 2009 are:\n1. \"Chappie\" (2015)\n\nThe number of feature films Neill Blomkamp directed before making \"District 9\" is 1."

> prior_films(1999, "american beauty")
[1] "Before directing the movie \"American Beauty\" in 1999, Sam Mendes directed the following feature-length movies:\n1. American Beauty (1999)\n2. Road to Perdition (2002)\n3. Jarhead (2005)\n4. Revolutionary Road (2008)\n\nThe number is: 4"

We can see it didn’t make up new movies. Instead, listed movies that came out after the movie in question. This is a great example of how LLMs are trained on language and not mathematical reasoning. It doesn’t understand the temporal sequence here of 2008 being after 1999 and thus couldn’t be before American Beauty.


A few takeaways:

  1. Again, we can see R and Python work together seamlessly.

  2. LangChain provides an LLM with tools, but this comes at greater cost; GPT 4 probably would have done much better here, but it would have cost much more money in context tokens.

  3. Prompt engineering is important: I could have been more explicit in the language Wikipedia tends to use, I could have asked it to use a calculator to check that the years didn’t difference out to below zero (e.g., 1999 - 2008 < 0), and I could have asked it to ignore silent films (even though the first Best Picture winner had no dialogue).

  4. Domain expertise remains huge in data science: I think I’m pretty knowledgeable about film, but I don’t know the silent era. I wasn’t aware how many of the early directors had many dozens of silent films. I didn’t know about quota quickies. Understanding domain knowledge is vital for a data scientist.

  5. KEEP HUMANS IN THE LOOP. What I did here is kept myself in the loop by checking performance against 100 hand-coded examples. This is a very nascent field using technology that has only been available to the public for a few years. Keep humans in the loop to make sure things don’t go off-track. For example, I won’t be adding these data to my model due to the error being too great.

To leave a comment for the author, please follow the link and comment on their blog: Mark H. White II, PhD.

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