This is bit of rambling, responding to Bethany Nowviskie's terrific "Don't circle the wagons", itself a response to Miriam Posner's "Some things to think about before you exhort everyone to code".
I'm a middle-aged, white, male programmer, so that's where I'm coming from. I can't help any of that, but doubtless it colors my perspective.
First, I have to say that the idea of coding being associated with prestige (as it seems now to be in DH) is rather foreign to my experience, but the rise of the brogrammer is probably a sign that in general it's not such a marginal activity anymore. These guys would probably have gone and gotten MBAs instead in years past.
DH is slightly uncomfortable territory for programmers, as I've written in the past, at least it is for people like me who mostly program rather than academics who write code to accomplish their ends. I speak in generalities, and there are good local exceptions, but we don't get adequate (or often any) professional development funding, we don't get research time, we don't get credit for academic stuff we may do (like writing papers, presenting at conferences, etc.), we don't get to lead projects, and our jobs are very often contingent on funding. All this in exchange for about a 30% pay cut over what we could be earning in industry. There are compensations of course: incredibly interesting work, really great people to work with, and often more flexible working conditions. That's worth putting up with a lot. I have a wife and young kids, and I'm rather fond of them, so being able to work from home and having decent working hours and vacation time is a major bonus for me.
None of that in any way accounts for the gender imbalance that Miriam is highlighting, though it does perhaps work as a general disincentive (in academia) to learn to code too well. I'd also say that there is nothing that can make you feel abysmally stupid quite like the discipline of programming. Errors as small as a single character (added or omitted) can make a program fail in any number of weird ways. I am frequently faced with problems that I don't know ahead of time I'll be able to solve. Ostensibly hard problems may be dead simple to fix, while simple tasks may end up taking days. It keeps you humble. But I would say that if you're the lone woman sitting in a class/lecture/lab, and you're feeling lost, you're not the only one, and it has nothing at all to do with your gender.
As Bethany cautions, please, please don't circle the wagons. It's my contention that most of the offensive things about programmer culture are not intentional nor deeply ingrained but are actually artifacts of the gender/race imbalance.
Programmer culture is exclusionary though. Undergraduate CS programs have "weed out" courses. I've actually taken a couple of these, and the first one did weed me out—it managed to be hard and extremely boring at the same time. I only came back to it years later. This gets at an aspect of programmer culture though, a sort of "are you good enough?" ethic. It's not without foundation—a lot of people who self-identify as programmers can't program—but it also means that when you start to work with a new group, there's often a kind of ritual pissing contest where you have to prove your worth before you're treated as an equal. This kind of thing is irritating enough on it's own, and it's easy to imagine it taking on sexist or racist overtones.
Programming also tends to squeeze out older folks. Actual age discrimination does happen, but it's also because staying current means almost totally rebooting your skillset every few years. The Pragmatic Programmer book recommends learning a new language every year, and this is crucial advice (my own record is more like one every 18 months or so, but that's been enough so far). If you let yourself get comfortable and coast, or go into management, your skills are going to be close to worthless in about 5 years. And, while your experience definitely gives you an edge, you're not guaranteed to have the best solution to any given problem. The 22-year-old who read something on Hacker News last night might have found an answer that totally blows your received wisdom out of the water.
[As another aside, the speed at which skills go stale means that any organization that doesn't invest in professional development for their programmers is being seriously stupid. Or they expect their devs to leave and be replaced every few years.]
The upshot is that the population of programmers not only skews male, it skews young. Put a bunch of young men together, particularly in small groups that are under a lot of pressure (in a startup, for example), and you get the sorts of tribal behaviors that make women and anyone over 35 uncomfortable. There's not just misogyny, there's hostility towards people who might want to have a life outside of work (e.g. people who have spouses and kids and like spending time with them). And this is both a cause of sexual/racial/age imbalance and a result. It's a self-reinforcing cycle.
But there isn't really one monolithic "coder culture", there are lots of them. Every company and institution has its own culture. Teams have cultures. Basically, any grouping of human beings is going to develop its own set of values and ways of doing things. It's what people do naturally. The leaders of these groups have a lot to do with how those cultures develop, but they aren't necessarily in any position to remedy imbalances.
Once you're in a position to hire people, you realize that hiring good developers is hard. In any pool of applicants, you're going to have a bunch of totally unsuitable people, a few maybes, and if you're lucky, one or two gems (or people you think might become a gem with a little polishing). Are any of these going to be women? Not unless you're really lucky, because the weeding out has already done its work. So once you're in a position to decide who gets hired, it's too late to redress any imbalance. The imbalance is not because leaders don't want to hire women, it's already there.
The only answer I can see is to get a lot more women into programming. If the CS curricula can't do it, maybe new modes like DH can. From what I've seen the gender balance in DH, while still not great, is a lot less ruinous than in programming in general, and a CS degree is far from the only road into a programming career (I don't have one). I think the cycle can be broken. I don't think there's a lot of deeply ingrained misogyny or racism in coding culture. Rather, it's a boys club because it happens to be mostly boys. If there were more women it would adjust. And I don't think that (mostly) it would put up much resistance to an influx of women. So circling the wagons is the exact opposite of what needs to be done.