Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
H, W = map(int, input().split())
a = [list(input())[: -1] for _ in range(H)]
c = H + W - 1
class FordFulkerson:
    def __init__(self, N):
        self.N = N
        self.G = [[] for i in range(N)]

    def add_edge(self, fr, to, cap):
        forward = [to, cap, None]
        forward[2] = backward = [fr, 0, forward]
        self.G[fr].append(forward)
        self.G[to].append(backward)

    def add_multi_edge(self, v1, v2, cap1, cap2):
        edge1 = [v2, cap1, None]
        edge1[2] = edge2 = [v1, cap2, edge1]
        self.G[v1].append(edge1)
        self.G[v2].append(edge2)

    def dfs(self, v, t, f):
        if v == t:
            return f
        used = self.used
        used[v] = 1
        for e in self.G[v]:
            w, cap, rev = e
            if cap and not used[w]:
                d = self.dfs(w, t, min(f, cap))
                if d:
                    e[1] -= d
                    rev[1] += d
                    return d
        return 0

    def flow(self, s, t):
        flow = 0
        f = INF = c
        N = self.N
        while f:
            #print(f)
            self.used = [0]*N
            f = self.dfs(s, t, INF)
            flow += f
        return flow
flk = FordFulkerson(H * W * 2 + H + W + 1)
b = H * W
s = 0
t = 0
for i in range(H):
  for j in range(W):
    if a[i][j] != ".":
      flk.add_edge(b + i * W + j, b * 2 + i, c)
      flk.add_edge(b * 2 + i, i * W + j, c)
for j in range(W):
  for i in range(H):
    if a[i][j] != ".":
      flk.add_edge(b + i * W + j, b * 2 + H + j, c)
      flk.add_edge(b * 2 + H + j, i * W + j, c)
for i in range(H):
  for j in range(W):
    if a[i][j] != ".":
      flk.add_edge(i * W + j, b + i * W + j, 1)
    if a[i][j] == "S": s = b + i * W + j
    if a[i][j] == "T": t = i * W + j
if (s - b) % W != t % W and ((s - b) // W != t // W): print(flk.flow(s, t))
else: print(-1)

Fixed submission:
import sys
input = sys.stdin.readline
H, W = map(int, input().split())
a = [list(input())[: -1] for _ in range(H)]
c = H + W - 1
class FordFulkerson:
    def __init__(self, N):
        self.N = N
        self.G = [[] for i in range(N)]

    def add_edge(self, fr, to, cap):
        forward = [to, cap, None]
        forward[2] = backward = [fr, 0, forward]
        self.G[fr].append(forward)
        self.G[to].append(backward)

    def add_multi_edge(self, v1, v2, cap1, cap2):
        edge1 = [v2, cap1, None]
        edge1[2] = edge2 = [v1, cap2, edge1]
        self.G[v1].append(edge1)
        self.G[v2].append(edge2)

    def dfs(self, v, t, f):
        if v == t:
            return f
        used = self.used
        used[v] = 1
        for e in self.G[v]:
            w, cap, rev = e
            if cap and not used[w]:
                d = self.dfs(w, t, min(f, cap))
                if d:
                    e[1] -= d
                    rev[1] += d
                    return d
        return 0

    def flow(self, s, t):
        flow = 0
        f = INF = c
        N = self.N
        while f:
            #print(f)
            self.used = [0]*N
            f = self.dfs(s, t, INF)
            flow += f
        return flow
flk = FordFulkerson(H * W * 2 + H + W + 1)
b = H * W
s = 0
t = 0
for i in range(H):
  for j in range(W):
    if a[i][j] != ".":
      flk.add_edge(b + i * W + j, b * 2 + i, c)
      flk.add_edge(b * 2 + i, i * W + j, c)
for j in range(W):
  for i in range(H):
    if a[i][j] != ".":
      flk.add_edge(b + i * W + j, b * 2 + H + j, c)
      flk.add_edge(b * 2 + H + j, i * W + j, c)
for i in range(H):
  for j in range(W):
    if a[i][j] != ".":
      flk.add_edge(i * W + j, b + i * W + j, 1)
    if a[i][j] == "S": s = b + i * W + j
    if a[i][j] == "T": t = i * W + j
if (s - b) % W != t % W and ((s - b) // W != t // W):
  if sum([x.count("o") for x in a]) == H * W - 2: print(min(H, W) * 2 - 2)
  else: print(flk.flow(s, t))
else: print(-1)